Moses suffered a dislocated shoulder in the 2-0 defeat at Arsenal in the Carling Cup on Tuesday.
Martinez said: “Victor fell very awkwardly and straightaway you could see that he had dislocated his shoulder.
“We sent him straight to hospital, and we’ll continue to assess him.
“Unfortunately we are looking at anything between four to six weeks, and that’s a shame because he looked very sharp.
“We know how much we’re going to miss Victor for the next few weeks. Injuries and suspensions are a reality of the game, and we have to adapt to it as well as we can.”
