Liverpool striker Roberto Firmino could be out for more than four weeks with a hamstring injury.
Fimino, 30, who has scored four goals in eight Premier League games this season, picked up the injury in Wednesday's 2-0 Champions League win over Atletico Madrid.
Manager Jurgen Klopp said losing the Brazilian was "a blow".
"We are talking weeks, still. More than four. I'd consider that a serious injury," said the German.
Midfielder Curtis Jones and defender Joe Gomez have also been ruled out of Sunday's trip to West Ham.
"Curtis is a completely different story [to Firmino]," said Klopp.