The 20 year old has been out of action for the Red Devils since suffering a double leg break against PSV Eindhoven in Champions League in September.
"I have always said to Luke that he can play in the final to keep his motivation high, but now I cannot say that anymore because we are in the final," said the Dutchman, speaking at press conference ahead of Sunday's final Premier League fixture against Bournemouth.
"It is a pity because he cannot reach that level to play. He needs more time to play but it keeps his motivation very high.
"It is still high and I have to give compliments to him because it is not easy to be away for such a long time. He is coming back, but he is coming back next season."
"Darmian is still out but can be in. It is dependable on the progress. Schweinsteiger is out and Shaw is out," said Van Gaal.
"Ashley Young is coming in, so he is restored of his injury and can train tomorrow with our squad. But it is one training session.
"Unfortunately Januzaj has been injured in the training session on Monday, so he is out for Sunday. We have to wait and see for the final."