Kevin Nolan could miss six weeks with a fractured shoulder, West Ham boss Sam Allardyce has confirmed.
Nolan damaged his shoulder in training on Thursday and missed the Hammers' 3-1 Premier League victory at Crystal Palace on Saturday.
Manager Allardyce admitted the Hammers will miss captain Nolan's influence, but backed "the best and strongest squad I've put together at the club" to handle his absence.
"Kevin fractured his shoulder and that's a massive blow to us, along with all the other players we've got injured," said Allardyce.
"He will be out for probably six weeks I would think.
"It isn't a dislocated shoulder, it's a fractured shoulder, but I don't know just how long that will keep Kevin out.
"We dealt with it brilliantly at Palace and let's hope we can continue to do that.
"It didn't affect us at Palace and maybe that's a sign there's more to come."
Mauro Zarate's volleyed debut goal set West Ham en route to victory at Selhurst Park, with Stewart Downing and Carlton Cole also on target.
West Ham were missing Matt Jarvis, Andy Carroll, Carl Jenkinson and James Collins at Palace, as well as Nolan.
Allardyce believes the comfortable victory indicates his squad's strength in depth.
"We were missing five players who play a big part in our squad, so to win the game comfortably with as many injuries as that was extremely pleasing.
"So perhaps this might be the best and strongest squad I've put together at the club - I hope it is."
West Ham host Sheffield United in the Capital One Cup on Tuesday night - the first time the clubs have met since the Carlos Tevez controversy.
Tevez's winning goal against Manchester United kept West Ham in the Premier League on the final day of the 2006-07 season.
West Ham's survival came at the Blades' expense, with Sheffield United launching legal challenges to Tevez's eligibility.
The Hammers were eventually forced to make payouts to the Blades after the Argentina striker was deemed ineligible due to third-party ownership rules.
Aware deep feelings still linger between the clubs, Allardyce admitted he would target victory on Tuesday for the West Ham faithful.
"I think the reaction is to get a team out there that wins, that's what the fans want us to do on the basis of that situation that arose at that particular time," he said.
"I'm not so sure how guilty Sheffield United were on it, but that's really nothing to do with me.
"It's about me making sure that they go home happy on Tuesday because they feel aggrieved about what Sheffield United did, so if I can do that for them it will be great."