Southampton say they have "reluctantly agreed" to let director of football Jason Wilcox join Manchester United.
The two clubs came to an agreement on an "acceptable compensation fee" to allow him to complete the move.
The former Blackburn Rovers and England winger, 53, joined the Championship club last summer.
Wilcox joins United as technical director, where the club said he "will work with all technical areas of the football department".
He had spent 11 years at Manchester City, where he was academy director before moving to the South Coast side.
"Whilst the club is naturally disappointed that Jason's stay at Southampton has only lasted nine months, it wishes him well for the future," Southampton announced in a statement.