The England international has been linked with a move to Chelsea this summer and saw two bids from the Blues rejected by the English champions.
"I felt he played very well the other night [against Chelsea] and he's looking in good condition and is mentally in good shape too," Moyes told reporters.
"We'll do everything we possibly can to keep that going and need him to keep performing well. At the moment he's in good shape. We told you (reporters) and everybody else from day one [that the player is not for sale], so I don't think there's anything else to add.
"Wayne Rooney has been a great player for many years for Manchester United. He was an up-and-coming great player as a young boy at Everton and his career has gone the way that people expected it to go."
United have picked up four points from their opening two matches in the league so far this season.