United are also understood to have written off £6.7m on ex-Germany captain Bastian Schweinsteiger.
They have not said the sum relates to the midfielder but it is understood he was only named in their domestic squad because of Premier League rules and is very unlikely to play for United again.
The Old Trafford club posted record annual revenues of £515.3m on Monday.
Van Gaal and his coaching team were dismissed 48 hours after leading United to victory over Crystal Palace in the FA Cup final.
Assistant manager Ryan Giggs subsequently left following Jose Mourinho's appointment as Van Gaal's replacement.
Mourinho left Schweinsteiger out of his Europa League squad and has told the 32-year-old he has only the remotest chance of playing this season, because the Portuguese manager will promote youngsters into his squad should injuries or suspensions affect his central midfielders.
It is now known that the former Bayern Munich player only retains that chance because Premier League rules forced United to name any player over the age of 21 in their squad if they had room within their allotted 25 places.
The situation surrounding the German - originally signed for a fee believed to be in the region of £11m - means United no longer think they will get their money back on the player, so have written off the £6.7m they had been valuing him at.
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Manchester United paid out £8.4m to former boss Louis van Gaal and his coaches after they were sacked in May.