David Brooks will be out for over a month, though captain Steve Cook is available for Wednesday match with Cardiff City.
Wales international Brooks missed the weekend trip to Queens Park Rangers, with head coach Jonathan Woodgate detailing the situation in his pre-match press conference.
"It's his other ankle," He explained. "He went over on it in training on Friday. We've had a scan on it, I think it's going to be four to five weeks.
"That isn't great as he's a valuable player at the football club."
Also on the sidelines has been Cook, who has been nursing a groin injury, though Woodgate said that his recovery and availability for selection has come quicker than expected.
"Cookie's fine, he's got some healing powers by the way. He pulled his adductor against Nottingham Forest and now he's fit to play, I've never seen anything like it to be honest," he said.
Remaining in the treatment room are Jack Stacey and Dominic Solanke, with the head coach offering the latest on their expected returns in the not-too-distant future.
"Jack Stacey, it's too soon for him," said Woodgate. "He should be another ten days or two weeks.
"Dom trained with the physios yesterday and should be back in training on Thursday. That's a huge bonus for the team and for me personally.
"I've followed his career throughout when he was at Chelsea, Liverpool and now Bournemouth, I know what kind of striker he is and I'm really looking forward to working with him.
"To get these results without your top striker is even better so hopefully we'll be an even better team when Dom plays as well."