"We have three games left," McCarthy said during his weekly press conference. "Yes, I would think it'd be safe to say he'll be back for the playoffs."
A league source told NFL Network's Albert Breer that Jennings sprained his left medial collateral ligament.
McCarthy said Jennings was at the Packers' team facility Monday and in good spirits.
"He's upbeat," McCarthy said, "He was in here for treatment, had a process to go through it with the medical staff."
The injury to Jennings also raised the question of whether or not the Packers planned to rest key players during the season's final weeks, provided they lock up home-field advantage throughout the playoffs this Sunday with a win over the Kansas City Chiefs.
But losing Jennings will be a significant -- if only temporary -- blow to a team best known for its dominant passing game.
"We feel fortunate that it is only a couple weeks," McCarthy said.
McCarthy said he has had conversations with general manager Ted Thompson about the team's strategy in such a situation, but he gave no indication of what the organization's philosophy is. Packers defensive tackle B.J. Raji doesn't believe McCarthy will make any changes in the midst of a 19-game winning streak that dates to last season.
The Packers also are monitoring several other injuries this week.
Defensive lineman Ryan Pickett and backup running back Brandon Saine both left Sunday's game with concussions. McCarthy is optimistic both players will be available this week, but they first will have to clear post-concussion testing protocols.
The Packers also are missing veteran left tackle Chad Clifton, guard Josh Sitton, running back James Starks and inside linebacker Desmond Bishop. McCarthy said Sitton (knee) is "making progress" and might practice this week. Bishop (calf) is "close" to returning, and McCarthy said he was hopeful Starks (right knee/ankle) could practice Wednesday.
McCarthy hasn't given up on getting back Clifton (hamstring/back), who has been out since Oct. 9. McCarthy said Clifton might be able to return to practice next week.
The Associated Press contributed to this report.