Jennings was injured following a 12-yard run with just under 14 minutes to go in the first half. After Jennings was tripped up, Buffalo linebacker Nick Barnett landed on him.
Jennings was able to walk off the field under his own power before being escorted to the locker room. He finished the game with 20 yards on eight carries.
Montell Owens ended up as the Jaguars' top rusher in the 34-18 loss, gaining 29 yards on seven carries.
The Jaguars were already missing running back Maurice Jones-Drew because of a foot injury.
Bills receiver Stevie Johnson left in the third quarter because of a left hamstring injury, and Buffalo starting offensive lineman Chris Hairston was carted off in the third quarter because of a right ankle injury.
Johnson scored on a 13-yard catch earlier in the quarter before leaving the game.
Information from The Associated Press was used in this report.