Jarrod Bowen will miss the first leg of West Ham's Europa League quarter-final against Bayer Leverkusen on Thursday because of a knee injury.
The forward, who has scored 19 goals this season, sustained the injury against Wolves on Saturday and might also miss the return leg on 18 April.
"Jarrod isn't with us. He's twisted his knee and there's some sort of damage," said Hammers boss David Moyes.
"We can't give any dates of when he might be back, unfortunately."
Bowen came off after 54 minutes during the win at Wolves and has been a key player for West Ham this season.