Rio Ferdinand is battling to save his Manchester United career after a calf injury ruled him out for the season.
The Telegraph says Ferdinand's injury problems in recent seasons have become a genuine cause of concern for manager Sir Alex Ferguson.
The United manager has consistently stated his belief that a strong central defensive partnership provides the foundation stone for all successful teams and Ferdinand's injuries have placed doubt at the heart of the area viewed as most crucial by Ferguson.
Ferdinand's United contract expiring in June 2013, time remains on his side to put his three-year injury misery behind him.
