The Hammers are set to take on Tottenham after the international break came to a conclusion.
However, the former Borussia Dortmund striker is not fit and may miss more than one game.
“Fullkrug is out, and he is continuing to recover from his injury, but the rest I hope will be able to feature,” Irons boss Julen Lopetegui told reporters on Thursday.
“I am going to meet with them this afternoon, but we don’t have bad news about them.
“The problem is that Niclas had one minor injury at the start, but there’s been a bit of a complication with this injury, and we are waiting for him to recover.
“It’s true that we thought he would be out for two weeks maximum, but it’s been a month and a half. Hopefully he will be ready for the next matches, but right now he is out.
“It is true that we had a lot of players in different countries (on international duty), and right now not all of the players have returned. I am going to see the last of the players today and tomorrow, so until the last moment we are not going to be together.
“It is always difficult to prepare for the matches (after a break), but it happens to a lot of teams and not only us. We have to manage this and be ready for the next match against Tottenham.”