The Dutchman is less than 12 months into a three-year deal at Old Trafford and has previously revealed that the job would be his last in management.
However, the former Bayern Munich and Barcelona boss stated that does not necessarily mean that retirement is on the horizon.
"Yes [this will be my last club] but there could be five years to go yet," he said in quotes carried by the club's official website.
"I can extend my contract. I've signed for three years because in three years you can build something. When Manchester United ask me to extend, then I shall decide. But this is my last club."
United are locked in a battle with several clubs for a place in the Premier League top four, including against fierce rivals Liverpool.
Van Gaal was heavily linked with a move to Anfield as director of football in 2012, before Brendan Rodgers was appointed as manger.
Speaking on the links, he added: "It was flattering, it is always pleasing to be contacted by a leading club, and Liverpool have a very good record in history.
"But I am the coach of United now, I can only speak about Liverpool as an opponent. It is not so interesting any more, it is in the past.
"It was the same with Tottenham last week. I have spoken to a lot of clubs but it is not good for Liverpool, Tottenham or for me to reopen things that are in the past."
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