Everton must wait to discover the extent of Mikel Arteta's hamstring injury after the influential midfielder was withdrawn early on in his side's 1-1 draw with Birmingham.
Arteta, who was named captain for the game in the absence of Phil Neville, had to be substituted after sustaining the problem in a chase with Sebastian Larsson.
Asked how Arteta was, David Moyes said: "I don't know, I just saw him come off. Obviously it looks like a hamstring injury but I haven't had a chat with the medical team yet to see what they think."
Moyes, who paid tribute to Arteta after his inspirational performance in the 2-1 win over Newcastle, felt the loss of the midfielder had made it difficult against Birmingham.
"It was a big blow for us because we needed some creativity and I knew that if we didn't have him, we would be struggling to create too much," Moyes said. "Leon Osman did, but we were struggling otherwise really to make anything happen.
"It was a bit frustrating. We didn't play well enough probably to win the game, but we had a few half chances."
Birmingham boss Alex McLeish praised his team's resilience in securing a point that moved them out of the relegation zone.
Blues had taken a 17th-minute lead at Goodison Park through Jean Beausejour's header but John Heitinga rifled in an equaliser ten minutes before the interval and the Toffees looked by far the more likely side to find a winner in the second half.
McLeish's men held on for the 1-1 draw, though, taking them up to 17th in the table, with West Ham dropping into the bottom three.
"I think that is an apt way to describe it - a battling point," McLeish said. "We started very brightly and got the opening goal. Then the players showed that tremendous resilience that they have."
He added: "We tried to be a little bit more predatory, but we never really had the composure in terms of the passing in the second half, but sometimes you need to get points in an ugly fashion."
Birmingham were forced into a substitution within the first ten minutes as David Bentley came off with what McLeish confirmed was a groin problem.
"He came in before the warm-up was finished saying that he felt a twinge but felt he could start, but clearly he wasn't okay," McLeish said. "So it will probably be a scan for him tomorrow and we'll know the extent on Friday."