Gronkowski still is considering whether to play the upcoming 2018 season, and has had "good communication" with the Patriots, per the source.
Gronkowski has a $250,000 workout bonus in his contract for 2018, which is paid out based him on attending 90 percent of the voluntary workouts.
Brady also is not expected to attend the start of the offseason program; he has been on a business trip to Qatar. In other years, Brady has been a regular participant at the team's offseason program, but he will miss at least the beginning this year.
"We have the voluntary offseason program that starts on Monday," Patriots coach Bill Belichick said last week. "It will be heavily attended, but I know there are a couple players that I've talked to that have other commitments, but that's the way it always is. So, not really anything new there."
Information from ESPN's Mike Reiss was used in this report.