Luhukay admitted United were looking at the striker and it would be tough to stop him leaving if they make a serious bid.
Luhukay said: "It's a decision George will have to make himself.
"I think it's really difficult when a club as big as Manchester United has an interest in him to say no.
"George must decide how he sees his future and I respect that. A good decision or not a good decision, I cannot answer that."