United have confirmed that Ji-sung Park has had a "complicated cartilage operation" and will consequently not play again until next season.
The club issued the following statement on Saturday morning:
"Ji-sung Park has had a complicated cartilage operation that required an expert in the field.
"He will be out for the rest of the season and we will assess the situation in August."
Park is in the care of world-renowned knee specialist Dr Richard Steadman in America. Dr Steadman's previous patients include Ruud van Nistelrooy and Michael Owen.
Sir Alex said on Friday: "We have not been able to get to the bottom of the injury. He was initially examined by our own physios but with these situations, if you have complications you send the player to a specialist - the best in the world.
"We either had to operate or let nature take its course. Because there was no clear reason for the injury, we knew it was bad enough for us to be concerned, which is why he has gone to America. Unfortunately, it puts an end to his season."
Park has not played since sustaining the injury during the March win over Blackburn.