The Dutch full-back left the field on a stretcher during the first half of his team's 3-1 win at Crystal Palace on Monday.
Speaking after Sunday's 1-1 Premier League draw against Everton, Sunderland head coach Gus Poyet confirmed Van Aanholt must go under the knife.
"Unfortunately Patrick is going to need an operation which means he is going to be out for two and a half to three months," Poyet told the club's official website
"It is a big loss because he is a left-footed left-back and there are not too many of them in the world, but we will help him and we will have to cope with it."
Van Aanholt has made 11 appearances since joining Sunderland from Chelsea over the close season.
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