Albion stopper Dean Blackwell has been ruled out for a month by boss Steve Coppell after suffering a recurrence of hamstring trouble.
Blackwell made his comeback from a hamstring injury at Preston on Saturday, but the former Wimbledon centre half went off in the first half of the 2-2 draw.
"I would imagine Dean is going to be out for a month," revealed Coppell.
"It's right in the belly of the muscle. I noticed him tweak it about five minutes before he went down.
"I suspected then that he certainly wasn't going to do the 90 minutes, but the way he went down showed he had damaged it more than we thought."
Blackwell has just agreed a contract for the rest of the season after signing initially for a month.
"It's amazing how often that happens, the curse of signing a contract," Coppell said. "I don't know whether it's a relaxation thing in your body."
Kerry Mayo is poised to deputise again in the centre of a five-man defence at the City Ground tomorrow night, with Nathan Jones making his first start for over two months at left wingback.
Coppell also fears he could be without Bobby Zamora and Graham Barrett at Nottingham Forest tomorrow night.
Zamora is still struggling with Achilles and ankle injuries and a related hamstring problem while Barrett has missed the last two matches with knee ligament damage.
Paul Brooker is on standby for a return to the starting line-up if Coppell's first choice strike force miss out.
Coppell, mindful of Saturday's home game against Reading, said: "Bobby's chances are slim. We are hopeful of a really good recovery but, realistically, even if he was available for Wednesday then he wouldn't be for Saturday.
"It might well be we say miss out Wednesday so you have got a chance for Saturday, although there is no guarantee that he would be fit."
Arsenal loan signing Barrett picked up his injury at Wolves a fortnight ago.
"It is something he's had before and I think he's a little bit concerned about it," said Coppell. "He's been at Arsenal seeing Arsene Wenger to try and renegotiate his contract with them, so he has been having treatment there.
"They have scanned him and there is nothing major on the scan, but I think because he's had problems with it before he's a little bit wary of it.
"To be honest I'm a little bit disappointed that he's again probably not available for Wednesday."
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