The Scotland midfielder hasn't featured at all during Latics' pre-season programme because of back and knee problems.
"It's too early to tell at this stage, but it is an area of concern for us," Martinez told the Wigan Evening Post.
"James is progressing well, but slowly. The back is something that's been bothering him for a while, and when we came back from Austria he felt it a bit more. It's one of those injuries that doesn't stop you from training, but when you do work hard it has a delayed reaction - and those are always the most frustrating.
"You probably feel you can get away with doing little bits of training, and knowing James he is the kind of person who wants to do as much as he can.
"We need to make sure he continues to get the right recovery and the right treatment, and we'll take it day by day."