The France international was stretchered off in the 34th minute of the second round match at Upton Park and could now be out for an extended period of time with an anterior cruciate ligament problem.
"Our team news is that Alou Diarra got injured the other night and is not involved in the squad," Allardyce said of Saturday's Premier League clash with Stoke.
"It's more serious than we expected and it looks like an ACL reconstruction, unfortunately.
"That will probably finish his season, that is a big blow to us in squad terms. He was hoping to forge his way into the side this season but, obviously with the injury, now that won't be the case."
No Vaz Te bids yet
Allardyce also confirmed they are yet to receive any bids for striker Ricardo Vaz Te, who recently put in a transfer request.
"We've had no offers for Vaz Te yet but I'd expect that we have an enquiry for him in the next couple of days. If he wants to leave, he can," added Allardyce.
"But the offer has to be right for us."
Meanwhile, Allardyce admits he is happy with the club's start to the top-flight campaign, which has seen them pick up four points from their opening two matches.
But he has demanded his team be more ruthless in front of goal after they spurned some excellent chances to claim victory as they were held 0-0 at Newcastle last weekend.
"It's pleasing to have two league games without conceding, but our disappointment is that it's not six points," he said.
"It's our fault we didn't get the three points at Newcastle, it was there for the taking.
"In defensive terms though, two games in and Jussi Jaaskelainen hasn't had to make a save yet. Let's hope that he's in the same boat tomorrow.
"If he keeps a clean sheet, I think we'll win."