Mitchell, who missed all of last season with an ailing knee, was limited to conditioning during the team's offseason program. The Patriots' training camp begins on July 26.
Per the Boston Herald, Mitchell offered two-word answers when asked about his knee -- "I'm good" -- and about his availability for training camp -- "We'll see."
The news of fellow Patriots receiver Julian Edelman's four-game ban for violating the NFL's policy on performance-enhancing substances and the 24-year-old Mitchell's inability to practice are the latest blows to New England's wide receiving corps.
Mitchell, a fourth-round selection of New England in the 2016 NFL Draft, had a decent rookie campaign with 32 receptions for 401 yards and four touchdowns.
The 6-foot-1, 200-pounder had an expanded role in the second half of the season, reeling in all of his scoring passes over the final six games.
Mitchell also came up big in the dramatic come-from-behind win over the Atlanta Falcons in Super Bowl LI. He had six receptions for 70 yards as the Patriots rallied from a 25-point, second-half deficit before winning 34-28 in overtime.
The Patriots attempted to beef up the position in the offseason with the signings of Jordan Matthews and Cordarrelle Patterson and the addition of Braxton Berrios in the sixth round of the 2018 NFL Draft.