Rio Ferdinand faces a 10-day lay-off after being forced to pull out of Manchester United's victory over Stoke City with a recurrence of a back injury.
The centre-back was named on the team-sheet at the Britannia Stadium but was withdrawn minutes before the Boxing Day kick-off when the problem flared up and he was deemed unfit to start the game.
Ferdinand's place was taken by young Northern Ireland defender Jonny Evans and the England international has now been ruled out of the rest of the Christmas and New Year programme.
"We have to get to the root of this because he has had this problem too many times now," said Manchester United manager Sir Alex Ferguson.
"We have to get to the bottom of it. It will be a week to ten days and then he should be okay."
His injury means Ferdinand will miss Monday's visit of Middlesbrough to Old Trafford and the FA Cup third round tie at Southampton the following Sunday.
The defender, who would almost certainly have been rested for the first leg of the League Cup semi-final with Derby County on January 7, will now target the visit of Chelsea to Old Trafford four days later for his return.
That game now has added significance following United's victory at Stoke which came courtesy of Carlos Tevez's goal seven minutes from time.
United returned from winning the Club World Cup in Japan six points behind second-placed Chelsea with two games in hand and, with both clubs winning on Friday, the game at Old Trafford could be crucial in terms of the title race.
Ferguson admitted his English and European champions faced a tough task at Stoke after their exertions in the Far East and said he was relieved to see United claim a victory.
"At this stage of the season I think they are all good wins," he said. "Coming back from Japan I think we were all worried about how it was going to affect the team but the energy level was good. It was a difficult game but sometimes you have got be patient in games and we were patient.
"Hopefully we will look back on this and think it was a significant victory," the Scot added.
"If we get to New Year's Day and are just a couple of points behind, we'll be happy with that. The second half of the season, we will kick on a bit."
Stoke appeared capable of claiming the point that would have eased their relegation concerns until defender Andy Wilkinson was sent off after collecting a second yellow card following a clash with Cristiano Ronaldo.
The full-back will now miss the trip to West Ham United on Decenber 28 but Stoke assistant manager Dave Kemp bemoaned the fact referee Chris Foy had missed Ronaldo's earlier kick at Wilkinson that could easily have been punished by a red card.
"28,000 people saw it but the one person who matters didn't," said Kemp.