Sunderland will be without Jan Kirchhoff for another three months after he underwent knee surgery.
The midfielder suffered an injury in his side's 1-0 defeat to Chelsea on December 14 and missed last Saturday's 1-0 win over Watford.
Manager David Moyes has now confirmed Kirchhoff will be missing for up to 12 weeks, a major blow in Sunderland's battle against Premier League relegation.
"Jan had an operation during the week to repair his lateral meniscus," Moyes said ahead of the Boxing Day away match against Manchester United.
"At the moment we think it will be close to 12 weeks.
"We have got a few back in training - Javi [Manquillo] is doing a bit and Steven Pienaar is around as well, as is Billy Jones who is doing a bit.
"We are going to need them, though whether they will be available for the Manchester United game I'm not quite sure."
The match sees Moyes return to Old Trafford for the first time since being sacked as United manager in 2014.
"I'm looking forward to it, going back there," he said.
"It's a great place to be a manager and a great privilege to have managed that football club.
"We go there knowing Manchester United are finding some form - we have to try to stop them."
Sunderland are 18th in the table and have lost five of their last six league away matches.