The Bills took another blow to the defense with the loss of DE Chris Kelsay for the season. (US Presswire)

The Buffalo Bills defense has been much improved over the past month, but it'll have to finish the season without a veteran role player in DE Chris Kelsay. Kelsay was placed on injured reserve Wednesday so the Bills could add two players, CB T.J. Heath and G Keith Williams, to the roster as injury replacements.

Kelsay tore a ligament in his neck at a practice in early November and aggravated the injury upon briefly returning to the field in Week 12. It’s not severe enough to require surgery, but he will need more time to recover following the latest setback -- which is why the Bills felt they had to place him on IR.

“He felt great when he came back to practice and then it was just one little shot that got him again,” coach Chan Gailey said. “So I think we really have questions about how long this thing takes to heal. We gave it two or three [weeks] last time and it felt great and yet it was one little lick. So is it four, five or six [weeks]? How long do you have to wait? And I think it was just one of those we just can’t wait on it to see. It’s one of those unknowns, really. You don’t know how bad it is until he gets hit again.”

Kelsay was understandably disappointed to have his season come to an early end. The DE has missed only six games to injury in his 10-year career up until this point.

“We’ve been playing great defense the last few weeks, to be standing on the sidelines and watching it from afar, it’s disappointing,” Kelsay said. “I’m envious of those guys being able to go out there and contribute and do what we know we’re capable of doing. It’s the nature of our business and unfortunately I’m on the sideline right now.”

OL decisions to be made: With C Eric Wood (knee) out 2-4 weeks, the Bills have a decision to make later this week regarding their interior offensive line. Interior backup David Snow is set to enter the lineup with Wood out, but it remains to be seen whether he’ll play at C or RG. Current RG Kraig Urbik is a candidate to move to the pivot. “We’re going to work them both and I’m not sure which way that’ll go, to be honest with you,” Gailey said. “We’ll have to wait and see which way is the best way to go by the end of the week.”

Hairston out for Week 14: Wood isn’t the only offensive lineman that will miss Sunday’s game against the St. Louis Rams. RT Chris Hairston will be out with an ankle injury, which will push backup T Sam Young into the starting lineup. ““He’s not going to make it this week, we’ll have to see where this thing leads with him,” Gailey said of Hairston. “They’re still doing tests. They did tests again yesterday. It’s not looking good for now and to be honest with you we’re hoping to get him back for the last two.”

WR Johnson sits out Wednesday: WR Stevie Johnson sat out Wednesday’s practice due to his left hamstring injury. He worked off to the side with a trainer during the open portion of practice, but the Bills are taking the cautious route given the nature of hamstring injuries. “We think he’ll be there [Sunday], but he’s got that hamstring that he sustained in the game and he couldn’t finish the game,” Gailey said. “So we’ll see. We’ll rest him today to see if he can get well enough to go and do some things tomorrow, do a little bit more Friday and be ready to go Sunday. We’ll see.”

Practice update: Eight players were limited at practice on Wednesday -- WR Brad Smith (hamstring), CB Justin Rogers (foot), CB Leodis McKelvin (back), WR T.J. Graham (ankle), LB Nick Barnett (knee), RG Kraig Urbik (knee), CB Aaron Williams (knee) and DT Spencer Johnson (ankle). WR Donald Jones, who missed Sunday’s game with a calf injury, returned and was a full participant.

For more updates on the Bills, follow correspondent Mark Ludwiczak on Twitter@CBSBills and @MarkLud12.