Jarrod Bowen is expected to be out for around six weeks with the broken foot he suffered against Liverpool, Sky Sports News he understands.
The 28-year-old limped off in the 60th minute as Julen Lopetegui’s side were beaten at the London Stadium, with no time frame given for his return.
Bowen revealed he picked up the injury during the first half but tried to play on.
There were fears Bowen, who has scored six goals this season, could be sidelined for up to two months, but Hammers boss Lopetegui is hopeful the 28-year-old will be back in action much sooner.
“Unfortunately for us, yes, he has an injury,” Lopetegui said. “He could have played 30 minutes with this injury and now he has to rest and he has to recover.
“Let’s see, but it won’t be for a few days. It’s not good news for us, but it’s a moment for the other players we have.
“We are sure that Jarrod will recover faster because of his character, but the truth is that he will be out for the next few matches.
“Let’s see. I’d rather not talk about one number because we have to see how it develops in the coming weeks.
“Jarrod is one of our main players, for sure, and our captain as well. But now we have to be able to find a solution and it’s time for the other players to show that they are ready to help us and to make sure that their response is going to be good.
“That’s why we are looking for a speedy recovery for Jarrod, but in the same way, believing in the players who are in the squad and they will try to take advantage of this opportunity.”
Bowen is West Ham’s top scorer in the Premier League this season with five goals and has the most assists with four.
His injury comes as a significant blow for the under-pressure Lopetegui, who has struggled since taking over from David Moyes this summer.
West Ham are 13th in the Premier League with six wins in 19 games, and are eight points above the bottom three.
Tomas Soucek should take the captain’s armband for Saturday’s visit to Manchester City.
There was some positive news from the Hammers camp this week as Michail Antonio was released from hospital following a car accident early last month.
The 34-year-old striker underwent surgery on his broken leg and will need a long-term rehabilitation due to his injuries.
“Michail will certainly be out for a long time,” Lopetegui said. “But the good news is that he is home.
“He is enjoying his family and it is certain that he will try to recover as soon as possible, but we will not have Antonio for long.”
What games could Bowen miss? West Ham’s next matches
January 4: Man City (a)
January 10: Aston Villa (a) – FA Cup
January 14: Fulham (h)
January 18: Crystal Palace (h)
January 26: Aston Villa (a) – Live on Sky Sports
February 3: Chelsea (a) – Live stream Sky Sports
February 15: Brentford (h)
