Steve Sidwell is set for two months on the sidelines with a back injury.
Albion announced earlier this week that he would miss Saturday's game with West Brom but Seagulls boss Chris Hughton has now confirmed the midfielder is ruled out for longer.
Sidwell is yet to play this season and Hughton said: "We're certainly looking at a couple of months out.
"It's a blow firstly for him. He's a valuable member of our squad, particularly in that midfield area with Beram Kayal being out.
"When we lost Kayal, we thought about whether we should bring somebody in but our thinking was very much we had good numbers in there, with Steve Sidwell being one of them.
"It's a disappointment but we can work around it. Pascal (Gross) is primarily a midfield player who has played a little bit more advanced and Izzy Brown is back shortly."