"It's like getting that new toy at Christmas," Rivera said at the time. "You open up the box, and there's what you'd hoped for. But you also have to be wise and smart about when you play with it."
Apparently, the Panthers weren't working McCaffrey enough. Or in the right way.
After what some called a disappointing first season for the No. 8 pick of the 2017 draft, McCaffrey has emerged as arguably the best all-purpose back in the NFL as the Panthers head into December.
Seriously. Lost in Sunday's 30-27 setback to Seattle that extended Carolina's skid to three games and damaged its playoff hopes was a performance for the record books.
McCaffrey had a franchise-record 237 yards from scrimmage, becoming the first player in team history to top 100 yards rushing and receiving in a game and only the second player in the NFL to do so since 2011. He also became the first player in the NFL since Arian Foster in 2011 to top 100 yards rushing and receiving with a touchdown in each category.
McCaffrey's emergence goes beyond one game. With 757 yards rushing and 608 yards receiving, he is on pace for 1,101 yards rushing and 885 yards receiving. According to ESPN Stats & Information, only three players have reached that level, and one (Marshall Faulk) is in the Pro Football Hall of Fame. Faulk did it twice, once in 1998 and in 1999. Arizona's David Johnson did it in 2016, and Le'Veon Bell did it in 2014.
Should McCaffrey top 1,000 yards rushing and receiving this season, the company would be even more elite: Faulk in 1999 and Roger Craig in 1985 with San Francisco.
McCaffrey should have plenty of opportunities. He is taking 97 percent of the offensive snaps, the most among running backs since 2001, according to ESPN Stats & Information. That's a big jump from his 69.8 percent a year ago, when he shared the backfield with Jonathan Stewart, who was released during the offseason.
McCaffrey's closest competitors for overall snap percentage since 2001 are Chicago's Matt Forte (91.8 percent) in 2013 and Dallas' Ezekiel Elliott in 2018 (89 percent).
Houston wide receiver DeAndre Hopkins (99.5 percent) is the only player among running backs, wide receivers and tight ends who has taken a higher percentage of snaps than McCaffrey this season.
Need more proof of McCaffrey's rising production? He leads all NFL running backs with 71 catches on 82 targets for 608 yards and five touchdowns. New York Giants running back Saquon Barkley has 71 catches on 87 targets for 581 yards and four touchdowns.
There's no concern about McCaffrey (5-foot-11, 205 pounds) being overworked.
"What a fantastic player," Seattle coach Pete Carroll said after watching McCaffrey dissect his then-No. 10 defense. "He's just a fantastic player. It doesn't matter how big he is or how fast he is or whatever he is. He's just a great football player."
Hall of Fame running back LaDainian Tomlinson believes Le'Veon Bell -- despite his sitting out the Steelers' 2018 season -- and Los Angeles Rams back Todd Gurley are the top all-purpose backs in the NFL. But he would rank McCaffrey, Barkley and New Orleans' Alvin Kamara, the 2017 NFL Offensive Rookie of the Year, right behind them.
"There are no limits on what Christian can do," said Tomlinson, who finished his career fifth on the NFL's all-time rushing list (13,784 yards) and seventh in all-purpose yards (18,456).
Hall of Fame executive Bill Polian, now an analyst for ESPN, agreed -- but with a twist.
"He's Alvin Kamara-plus," Polian said.
But how's his durability?
One game into McCaffrey's rookie season, Rivera didn't want to "wear the batteries" out on the former Stanford star.
Rivera and offensive coordinator Norv Turner said 25 to 30 touches per game was realistic for McCaffrey this season.
Through 11 games, McCaffrey has reached 25 carries twice: Week 3, when he rushed for a career-best 184 yards on 28 carries and caught two passes for 10 yards in a win against Cincinnati, and this past week, when he had 17 rushes for 125 yards and 11 catches for 112 yards.
He's averaging 20.3 touches per game, which is still a big leap from his 12.4 touches a year ago, when his top rushing game was 15 carries for 66 yards against Atlanta.
"C-Mac is a ballplayer," quarterback Cam Newton said after the Cincinnati game. "It's hard for a lot of people to label him. They want to say he's this, but playing like today, he's obviously not just a receiving back. He's a total running back."
McCaffrey's durability and productivity, which were in question before the season, were big reasons the Panthers recently released running back C.J. Anderson, who was signed to complement McCaffrey. Anderson was getting less than 10 percent of the snaps.
“The thing that has impressed me the most, and I don’t want to jinx him, is his durability," Polian said. "That’s what everybody worried about in terms of him being the featured back. Could he hold up with as many touches as he gets?
“He’s been magnificent so far."
Now McCaffrey's complements are wide receivers DJ Moore and Curtis Samuel, who have opened things up for McCaffrey. One of McCaffrey's more balanced games this season came against this Sunday's opponent, Tampa Bay, when Moore and Samuel began getting more involved in the scheme. He rushed 17 times for 79 yards and two touchdowns and caught five passes for 78 yards.
"They've really tailored their offense around him and Cam," Buccaneers coach Dirk Koetter said of McCaffrey. "He's a smart player, has exceptional quickness, vision, cutting ability. And then as a route runner, you're not going to find many [that can do what he does]."
Tomlinson credits Turner, his offensive coordinator at San Diego as a rookie in 2001 and his coach with the Chargers from 2007-09. He reminded that this isn't the Turner who pounded the ball inside in '01 and used multiple backs in the passing game the second time around.
With McCaffrey, there is no need for multiple backs.
“Christian’s dexterity that he possesses is really incredible," said Tomlinson, who works as an NFL Network analyst. "It’s the perfect match with someone like Norv that knows how to use that skill set. He's a unique athlete in itself, but the way he excels is basically getting the ball into his hands in space, of letting him create certain runs, not necessarily forcing him to go downhill and try to use him inside the whole game.
“It’s really reminded me of the way he was used at Stanford."
In 2015, McCaffrey broke Barry Sanders' NCAA record for all-purpose yards by compiling 3,864 yards at Stanford. At the end of that season, he became the first player to top 100 yards rushing and receiving in Rose Bowl history.
“He’s translated his college game almost verbatim to the NFL, which truthfully rarely happens in a multitalented back," said Polian, who was the Panthers' general manager from 1995-97. "One strength usually always supersedes the other. But in this case, he had running, catching and blocking at Stanford, so it’s almost rare to have all three in the NFL, and he does.
“He’s a rare guy."
As No. 8 pick, pressure's on
Panthers defensive coordinator Eric Washington didn't have time to watch McCaffrey's performance against Seattle. He didn't have to watch to know things were going well.
"I just heard the roar of the crowd," Washington said.
Hunt, taken in the third round, led the league in rushing with 1,327 yards. Fournette was eighth with 1,040 yards. Kamara, also a third-round pick, had 1,554 yards from scrimmage and 14 touchdowns.
McCaffrey? He led all running backs with 80 catches, but his 2.4 yards per rush in the first eight games and 3.7-yard average for the season left some analysts questioning whether he could run between the tackles.
That, too, has been dispelled this season. McCaffrey's longest run from scrimmage -- 59 yards against Seattle -- came right up the gut.
"From Year 1 to Year 2, him as a runner, he looks more comfortable in the system," Tomlinson said. "You don’t see him pressing. Everything that happens for him looks natural. To me, his ability to handle everything Norv has thrown at him, that’s been the most impressive thing. That’s freaking incredible."
McCaffrey welcomed the extra work, knowing he had something to prove, even though he would never use that word.
"When they take you with the eighth pick, I don't want to say pressure, but you've got a lot of people counting on you," McCaffrey said. "So I knew [I] was going to be a pivotal point. But at the same time, I still have to earn everything. That's my mindset."
It's not about putting up big numbers or setting records for McCaffrey, and he made that clear after Sunday's record-setting day.
"That's all great, but I'd rather win," he said after the Panthers fell to 6-5 and out of the two NFC wild-card spots. "It sucks when you lose ... A lot of things I can do better."
He gets no argument from Polian.
“We had a saying when we were in Carolina. There are very few players that live up to as advertised," he said. "In any given draft, there might be 10 players you can put that tag on after two years, and he’s one of them."
ESPN Tampa Bay Buccaneers reporter Jenna Laine contributed to this report.