Reilly was hurt midway through the fourth quarter but returned for the Owls' next series in a 22-13 loss to Houston in the first American Athletic Conference game.
Reilly said his knee did not hurt badly when he left Lincoln Financial Field. However, later Saturday evening, the knee started to throb.
"There is so much adrenaline involved when you are playing the game," Reilly said. "I didn't feel it as much when I was playing. I didn't' want to let my teammates down, so I went back in the game.
"Later on that night, though, around 8, my knee was on fire. I knew it was worse than we originally thought."
While he was unable to participate in practice Tuesday, Reilly said the knee felt "pretty good" after the workout.
"I just needed a few aspirin and some ice," he said.
Granger, who started two games last season, wants the Owls to get on a roll. Dating back to last season, the Owls have lost seven of their last eight games. Their last win, a 63-32 victory over Army in November, came with Granger, a George Washington High School product, starting at quarterback.
While he had to be disappointed that he was not named the starter this season - Reilly never started a game before this season's opener - Granger has not talked extensively about it.
"It's been a challenge," Granger said. "But I have just tried to get better even if things didn't go my way. I can't control what decisions they make. I believe in me. I believe in the system. I want to go out and play quarterback and win."
After this weekend's home game, the Owls have a bye and do not play again until they visit Idaho on Sept 28.
Contact John N. Mitchell at firstname.lastname@example.org. Follow on Twitter @JmitchInquirer