The Red Devils go into the match on Sunday with a fourth-place spot already guaranteed, but Van Gaal refuses to name a weakened side against relegation candidates Hull.
United captain Rooney was ruled out of the last outing against Arsenal with a leg injury, while goalkeeper De Gea was taken off with a hamstring complaint.
Van Gaal is confident his skipper will start against the Tigers, but is not prepared to make a call on his shot stopper just yet.
Wayne is available, he is captain so he shall play
Louis van Gaal
The Dutchman said on the United duo: "Wayne is available, he is captain so he shall play.
"I don't know [if David will play at the moment]. He trained today but only with the goalkeeping coach.
"He still has a little problem but I'll wait a day longer as I want him to play against Hull City."