INDIANAPOLIS — Colts receiver Marvin Harrison underwent an MRI Wednesday and is questionable for Thursday night's game at Jacksonville, coach Tony Dungy said.

Harrison, who apparently hurt his knee against Detroit on Sunday, "actually has a hamstring issue," Dungy said Wednesday.

The availability of running back Joseph Addai and safety Bob Sanders will likely be gametime decisions, Dungy said.

Harrison underwent the MRI on Wednesday, and "I'd say he's questionable at this point. We'll have to see," Dungy said. "And, obviously, we're going to be cautious if there's any issues at all, as we will with Joseph and Bob."

Addai has been nursing a sore shoulder, which he injured Dec. 7 against Cincinnati, and did not play Sunday against Detroit. Sanders, whose right knee was swollen last month, also was held out of the Lions game.

He said both players have practiced with the team this week and want to play.

"They're excited about going. My sense is they'll play, but we'll see what happens," Dungy said. "We probably won't know until game time. It's going to be one of those things we'll probably have to wait and see."