The biggest injuries from NFL preseason Week 2

Week 2 of the NFL preseason was tough on quarterbacks, as both Buffalo and Philadelphia are dealing with injuries to potential Week 1 starters. Meanwhile, the Patriots lost one of their first-round picks for the season and the 49ers' starting running back could be sidelined until the regular season begins.

Here are the most important injuries that have occurred so far in the second week of preseason games:

Buffalo Bills

Quarterback AJ McCarron (broken collarbone)

Defensive tackle Kyle Williams (knee)

Prognosis: McCarron suffered a right shoulder injury, which is reportedly a hairline fracture to his right collarbone. Meanwhile, first-round pick Josh Allen looked good in a performance the Bills might need more of sooner than expected as Allen and Nathan Peterman remain in the QB mix. Williams left early in the second quarter because of an apparent right knee injury and walked to the locker room under his own power. He was later ruled out for the remainder of the game. -- Mike Rodak

Dallas Cowboys

Guard Zack Martin (knee)

Prognosis: The Cowboys lost the Pro Bowl guard in the second quarter to a knee injury. While the extent of the injury is not yet known -- he will undergo an MRI on Sunday -- head coach Jason Garrett said the doctors were somewhat optimistic, and owner and general manager Jerry Jones said: "I'm not thinking that Zack is problematic here." Martin is among the most valuable players on the Cowboys. Martin keeps the pocket clean for Dak Prescott and his run blocking plays a big part in Ezekiel Elliott's success. If the Cowboys lose Martin for any amount of time, Joe Looney has been the backup interior lineman the last two years, but they could consider tackles La'el Collins or Cameron Fleming inside. -- Todd Archer

Green Bay Packers

Running back Jamaal Williams (ankle)

Right guard Justin McCray (calf)

Wide receiver Jake Kumerow (shoulder)

Prognosis: Neither Williams nor McCray could say definitively whether they would've been able to return if it were a regular-season game but neither was concerned that the injuries would be long-term issues. Kumerow (shoulder) avoided a major injury and suffered only a sprained SC joint. That shouldn't impact his chances of making the 53-man roster. He has been one of the stars of the preseason for the Packers with a pair of touchdowns including Thursday's 82-yard catch-and-run score. -- Rob Demovsky

New England Patriots

Offensive lineman Isaiah Wynn (torn Achilles)

Prognosis: Wynn, who was making his preseason debut, was carted to the locker room in the first quarter after hobbling off the field, and it was later learned that he tore his Achilles and is out for the season. The 2018 first-rounder was working as the team's backup left tackle and the club had been experimenting with him at right tackle with the top unit over the last week. So the Patriots lose a player who was vying for a top-5 role on the line, but at the least, was going to be one of the seven linemen active on game day. This thrusts LaAdrian Waddle into the swing tackle role, with depth being tested behind him with Matt Tobin, Ulrick John and Cole Croston also at the position. -- Mike Reiss

Philadelphia Eagles

Quarterback Nick Foles (right shoulder strain)

Prognosis: Foles "should be fine" after suffering a mild shoulder strain against the Patriots, a source told ESPN's Adam Schefter, though it's uncertain if he'll miss any playing time. With Carson Wentz still working back from an ACL tear, Nate Sudfeld would get the start in the third preseason game against the Browns if Foles is sidelined, but it sounds as if Foles should be able to play in the regular-season opener if called upon. -- Tim McManus

Pittsburgh Steelers

Tight end Xavier Grimble (torn ligament)

Prognosis: Tight end Xavier Grimble will miss the rest of the preseason because of a torn thumb/wrist ligament that required surgery. Grimble is the team's No. 3 tight end who's a primary blocker but can use his athleticism to make plays vertically. He's hoping to be back for Week 1 but must see how the hand heals first. The Steelers are thin at tight end with Vance McDonald (foot) also out, leaving Jesse James as the only healthy tight end with an NFL catch. -- Jeremy Fowler

San Francisco 49ers

Running back Jerick McKinnon (calf strain)

Prognosis: McKinnon actually suffered his calf strain in practice last week but after initially being called week-to-week, McKinnon has now been ruled out for the rest of the preseason. That's not a surprising development, but the Niners believe he will be ready for the season opener against the Minnesota Vikings. With McKinnon and top backup Matt Breida (shoulder) not available for the rest of the preseason, the Niners signed veteran Alfred Morris last week. Morris enters a competition with the likes of Raheem Mostert, Joe Williams and Jeremy McNichols for one, possibly two, more running back spots on the depth chart. Given his experience, there appears to be an opportunity to nail down a job over the next couple of weeks, but the Niners remain confident that both McKinnon and Breida will be ready for Week 1. -- Nick Wagoner

Houston Texans

Cornerback Kevin Johnson (concussion)

Wide receiver Sammie Coates Jr. (concussion)

Prognosis: The Texans had two players leave the game because of a concussion: starting cornerback Johnson and wide receiver Coates. It is unclear how long either player will be in the concussion protocol. If Johnson is out for a significant amount of time, Aaron Colvin probably will play outside and Johnson Bademosi would be the Texans' third corner. Coates is competing to make the Texans' roster and has had a good training camp and preseason so far. -- Sarah Barshop

Minnesota Vikings

Cornerback Mackensie Alexander (ankle)

Prognosis: The Vikings' nickel corner exited Saturday's game in the first half because of an ankle injury. The team will conduct further tests to find out the severity, but if Alexander has to miss time, both Terence Newman and rookie Mike Hughes will be looked at to fill the void. Hughes has impressed early in the preseason with his ability to pick up the intricacies of the nickel position and Newman has plenty of experience in the slot to go around. The one thing the Vikings don't lack is quality depth at cornerback, which helps the situation with Alexander depending upon how much time he might have to miss. Alexander was one of several Vikings to suffer an injury Saturday. -- Courtney Cronin