Lukasz Fabianski was substituted off with a hamstring injury in the early stages of West Ham's clash against Sheffield United on Friday night.
With 13 minutes on the clock, Fabianski went down in distress clutching his hamstring after taking a goal kick, and was subsequently replaced by David Martin.
The Poland international has recently returned from a long-term hip injury and was playing his fourth game since his first start back on December 28.
"He felt something in his thigh, he was a big miss when we didn't have him before," said David Moyes after the game.
"I'm hoping that he won't be out for long, but obviously until we get the scans and everything done we won't be able to see conclusively what it is.
"I think it's been quite well documented that having another goalkeeper to choose from might be a good thing to have. Lukasz has been so good for the team when he's played, and we obviously missed him when he wasn't in."
Martin went on to gift Sheffield United the lead as his wayward pass to Fabian Balbuena was intercepted by John Fleck, leading to Oli McBurnie's strike which gave the hosts all three points in a 1-0 win.
West Ham are closing in on the signing of Middlesbrough goalkeeper Darren Randolph to provide back-up in goal with Spanish goalkeeper Roberto failing to impress in his seven-game stint between October and November.
Moyes is desperate to sign a new goalkeeper, although Randolph has been out of Middlesbrough's side since November because of a quadriceps injury.
Fabianski has established himself as the No 1 goalkeeper at West Ham since joining from Swansea last summer for £7m and has kept three clean sheets before his injury.