Bomber was carried off after picking up a knock on the outside of the ankle bone, and although an X-ray revealed no break, he is likely to be on crutches for the next few days with his ankle supported in a brace.
Caretaker boss Dennis Wise said: "It was a real blow to lose Harris on Saturday because he was looking really threatening and was convinced that he was going to score. Hopefully we'll have him back sooner rather than later."
Harris' injury leaves the Lions a bit short up front, with only Bob Peeters and Noel Whelan fit amongst the recognised first team strikers. However Kevin Braniff, who came on for Peeters against Burnley, should be able to provide ample cover while Harris recovers.