The 25-year-old featured in the first team during the club’s pre-season tour of the United States, but has twice been an unused substitute, despite a lengthy injury list at Old Trafford.
When asked to explain the absence of the Japan international, Van Gaal hinted that Kagawa had been dropped due to a disagreement over his best position on the pitch.
The former Netherlands boss was hoping to deploy Kagawa in a more withdrawn midfield role, something which the player did not agree with.
Van Gaal said: “Kagawa did not wish to fulfil my wishes, my philosophy when I played him in the United States.
“Kagawa was a No.10 at [Borussia] Dortmund but I want to try him at No.6 and No.8.”
Kagawa joined the Red Devils from Borussia Dortmund in July 2012 and made 30 appearances in all competitions last season.