Van Gaal played a key part in developing the 24-year-old at Bayern when was in charge at the Allianz Arena between 2009 and 2011.
However, Muller insists that he is happy to remain with the Bundesliga champions for the foreseeable future.
"It's not a secret that Louis van Gaal and I have a relationship that goes a bit further than a normal trainer-coach relationship," he told Sport Bild.
"I have a contract with Bayern Munich until the summer of 2017. I really enjoy playing for Bayern. There's not really anything better than this."
New United boss Van Gaal is understood to have around £150m to spend on players before the start of next season.