The 28-year-old Aussie has suffered renewed back and hamstring problems in training and is almost certain to leave Elland Road in the summer.
Gray told the club's official website: "Mark has had a recurrence of his back and hamstring problem and he will not play again this season. He trained yesterday and it just flared up again. If you believe the stories that are in the press then he has probably played his last game for the club, the physio has said he will require four weeks rest at least.
"It's not necessarily his last game but it looks that way. I think Mark is used to playing his football in the top-flight and he will want to continue to do that."
Viduka joined Leeds in the summer of 2000 from Glasgow Celtic and has scored 59 league goals in 130 games for United.