The Red Devils struggled at the start of the Premier League campaign and have only scored once after the hour mark in games this season.
Questions have been asked over the fitness of the team after they held on for wins in their last two games against West Ham United and Everton.
"Fitness is maybe a point, because I have already said that I have adapted my intensity of training sessions to a lower level," The Mirror quotes Van Gaal as saying. "But I have to give a certain level because they need to play 90 minutes.
"But I think we are fit enough because what I see of my players. They are fighting to the last minute and are willing to do everything, so I'm very happy with the passion of my players."
Tonight, United will take on West Bromwich Albion at The Hawthorns.