Michail Antonio has been ruled out of West Ham's crucial game against Leicester City on Sunday, with the Hammers fearing that the forward could miss a significant amount of their Premier League run-in.
Antonio was forced off after 36 minutes at Wolves on Monday and the hope was that it was not a serious issue.
However, while the 31-year-old is still being assessed by club medics who are seeking further clarity after initial scans, it is understood the damage to his hamstring is more significant than was initially hoped after the game at Molineux.
The Hammers sit fourth and are on the home straight of an unlikely push for Champions League football next season, but Antonio's injury will dent hopes of a top-four finish with eight games remaining before the end of the season on May 23.
West Ham host Leicester, Chelsea and Everton before the end of the season as they look to finish in the top four and cap a remarkable turnaround under Moyes.
However, the loss of Antonio - added to the absence of Declan Rice after the midfielder suffered a knee ligament injury with England - is a hammer blow to Moyes.
Antonio is the only senior striker in the squad at West Ham after Moyes elected not to waste money sign a striker that he was not totally convinced by in the January window.
The arrival of Jesse Lingard on loan has eased the attacking burden on Antonio, whose loss to hamstring problems was keenly felt earlier this season, while Jarrod Bowen replaced the forward at Molinuex on Monday and scored his second goal in as many games.
"If Jarrod plays as well as he did [against Wolves] up front, then that’ll help us, but we’re just beginning to run a little bit low on bodies at the moment," said Moyes.
The West Ham boss could also turn to young striker Mipo Odubeko, who has impressed at youth level but had little chance to show what he is capable of with the first team.
Arthur Masuaku lasted more than an hour on his return from knee surgery on Monday while Angelo Ogbonna, who has been missed at the back, is closing in on a return too and has been training this week.