West Ham manager Sam Allardyce has described Andy Carroll's continued absence through injury as a "great worry" and admitted he has no idea when the striker might be ready to return.
Carroll is yet to make an appearance for the Hammers this season after completing his permanent move from Liverpool.
Successive heel injuries have frustrated the 24-year-old striker's bid to make a comeback, and the medics overseeing his recovery remain unsure when he might be fit to rejoin Allardyce's squad.
"We've been trying to get a date out of the guys over in Amsterdam," Allardyce told Sky Sports News. "But they're reluctant to give us any clear indication of just how long it's going to be before he can join us back here and start training with the players, with the squad and then obviously getting into the team to play some games.
"It's obviously a great worry and concern for us all and one we haven't expected, but one we have to make sure we deal with."
West Ham have struggled for goals without Carroll with Allardyce often opting to play without a recognised striker. The east Londoners are one of the lowest scorers in the Premier League this season, having netted nine times in 11 games.
Allardyce revealed he had tried to improve his attacking options in the summer only to be rebuffed by his targets.
"We tried to sign four top strikers before the window shut in August, so we didn't just sit back and not try to sign the one player we felt would add to the situation," he said. "As I said, we tried our very, very best. David Sullivan and David Gold tried their very best to sign a top, top striker.
"Unfortunately, none of the players that we went for wanted to join West Ham at the time."