An ankle injury has Carolina Panthers center Ryan Kalil in danger of missing his first game since 2012.

The four-time Pro Bowler is listed as doubtful for Monday night's game against the Colts. A doubtful designation means there's at least a 75 percent chance a player sits, but coach Ron Rivera on Saturday said Kalil will be a game-time decision.

If he's ultimately ruled out, Kalil will be replaced in the starting lineup by versatile sixth-year veteran Fernando Velasco.

"[Kalil] was the one anchor last year. He was the one in the middle and he got everything going," Rivera said. "This year, the play of the two young guards has been outstanding. So you feel pretty comfortable that if something were to happen that he doesn't play, you have a guy that's going to be surrounded by guys who have been playing at a very high level for you."

Velasco started seven games at guard for the Panthers last year. He signed with the Titans this offseason but didn't make the roster. He then resigned in Carolina in Week 2.

Kalil hasn't sat out a start since he was placed on injured reserve after just five games in 2012 with a Lisfranc injury. Before then, he had played every game since 2009.

Rivera said Kalil isn't dealing with a high-ankle sprain, but Rivera wouldn't get into specifics. He still doesn't even know how it happened.

"I watched the tape [from the Eagles game] and I had completely forgotten about it, and when I watched it a second time, not with intent looking for it, I still didn't see it," Rivera said. "That's why I was so surprised when I heard about it."

Linebacker Shaq Thompson is also listed as doubtful for Monday night. It would be a surprise if he plays, but Rivera said the rookie "had a good day" Friday.

Fellow rookie Daryl Williams is set to play for the first time since he sprained his MCL on his first snap in Week 1. He suffered that injury on the field goal unit, but he should get some time with the offense as soon as Monday.

"He'll play some at the tackle position," Rivera said. "He's a young guy that we had hopes for and plans for and becoming a part of that. Again, you just never know if somebody else is going to get hurt, so you always want to make sure those young guys have gotten some quality reps.

"The plan is for him somewhere along the lines to get a series or two early and a series or two late, so hopefully in the first half you'll see him out there somewhere and then later in the first half."

PANTHERS	Injury	Thurs.	Fri.	Sat.
DE Mario Addison	Shoulder	DNP	DNP	DNP/OUT
DT Dwan Edwards	Ankle	DNP	DNP	DNP/OUT
C Ryan Kalil	Ankle	DNP	DNP	DNP/DOUBTFUL
LB Shaq Thompson	Knee	DNP	DNP	DNP/DOUBTFUL
FB Mike Tolbert	Not injury related	DNP	Full	FP/PROBABLE
LB Thomas Davis	Not injury related	DNP	Full	FP/PROBABLE
OT Daryl Williams	Knee	Full	Full	FP/PROBABLE

COLTS	Injury	Thurs.	Fri.	Sat.
C Khaled Holmes	Neck	DNP	DNP	DNP/OUT
WR Phillip Dorsett	Ankle	DNP	DNP	DNP/OUT
LB Nate Irving	Knee	DNP	DNP	DNP/OUT
S Winston Guy	Shoulder	DNP	DNP	DNP/DOUBTFUL
S Mike Adams	Hamstring	Limited	Full	FP/PROBABLE
S Clayton Geathers	Knee	Full	Full	FP/PROBABLE