The 20-year-old has been strongly linked with a move to Premier League rivals Sunderland.
But Van Gaal insists the Belgian winger is not for sale.
“I have 28 players and I have to select every week, and maybe every three days,” Van Gaal said in his pre-match press conference today.
“Last week I chose other players. He [Januzaj] is doing his utmost best – all the players are doing that. I don’t have any complaints.”