Manchester United manager Sir Alex Ferguson expects Jonny Evans to be out for two weeks with a calf injury, adding to club's defensive problems.
Evans was forced off at half-time in the
5-0 victory over Wigan
, leaving United without a fit centre-back.
"We have had a nightmare the last few days," said Ferguson. "Phil Jones and Chris Smalling have both been ill.
"Rio Ferdinand called off with a back injury and Jonny Evans has come off at half-time. It puts you under pressure."
With Nemanja Vidic a long-term absentee, Ferguson will be hoping Jones and Smalling recover for the visit of Blackburn on New Year's Eve, when a point would take United above Premier League leaders Manchester City for 24 hours at least.
Shorn of his recognised centre-backs, Ferguson was forced to improvise against Wigan with Michael Carrick moving into central defence and Patrice Evra shifting across to the middle following the departure of Evans.
Man Utd's current injury list
- Nemanja Vidic (knee)
- Darren Fletcher (illness)
- Rio Ferdinand (back)
- Michael Owen (thigh)
- Anderson (knee)
- Tom Cleverley (ankle)
- Fabio (hamstring)
- Phil Jones (illness)
- Ashley Young (knee)
- Chris Smalling (illness)
- Jonny Evans (calf)
Antonio Valencia played at right-back against his former club, and Ferguson was delighted with the performance of his patched-up rearguard.
"Carrick was magnificent, and Valencia never stopped going up that touchline," he said. "It was a fantastic performance from the two of them.
"I'm really, really pleased. Patrice Evra has been a great leader, showing the way forward for the players."
Ferguson also saluted the performance of Dimitar Berbatov, after the Bulgarian striker marked a rare start with a hat-trick.
"It was the right game for him," said Ferguson. "I needed his height for set-pieces against us and he's weighed in with a hat-trick. We're really pleased for him and it helps with confidence.
"Dimitar hasn't had the best of starts to the season in terms of selection given the options I have with [Danny] Welbeck, [Wayne] Rooney, [Javier] Hernandez, so I'm really happy for him."
After back-to-back 5-0 victories, United are now level on points with City, with just five goals separating the teams on goal difference.
"Fortunately our goals have come at the right time of the season," Ferguson said.
"We're really hitting good form now and there's a real goal threat about us from all departments.
"If we're top of the league or joint top with City by New Year's Day I'll be happy."