Saints defender to miss League Cup final
Van Dijk suffered the problem in Southampton's win over Leicester on January 22.
Van Dijk suffered the problem in Southampton's win over Leicester on January 22 and the Dutch centre-back won't return to action until late in the season.
That rules him out of Southampton's first League Cup appearance since 1979 as they bid to win the competition for the first time by beating United at Wembley on February 26.
"He will not be available for many weeks, two or three months," Southampton manager Claude Puel said on Thursday.
"It's an important problem and difficult for us. He is important for the group and the fans with his quality and leadership.
"It's a blow but we will find a solution. For the semi-final second leg against Liverpool we got a fantastic result without him and we will continue with other possibilities.
"Ryan Bertrand can play in this position, and we will see with young players like Jack Stephens. We have possibilities."