Arsenal's torrid week continued this afternoon when Arsene Wenger revealed that Per Mertesacker has been ruled out "long term".
Adding to Wenger's defensive problems is that Laurent Koscielny is also missing for tomorrow's FA Cup fifth-round tie at Sunderland because of a knee problem.
But while Koscielny should recover in a week from the injury sustained during Wednesday night's painful 4-0 drubbing by AC Milan, Mertesacker may have played his last game this season.
The German international suffered ankle ligament damage during Saturday's Barclays Premier League victory against Sunderland that requited ankle surgery.
"Unfortunately he has had surgery and we have lost him for a while," Wenger told the club's official website, www.arsenal.com.
"How long I don't know. He had reconstruction of his ligaments, so it will be long term."
Koscielny limped off shortly before half time at the San Siro, but the prognosis on his injury is far more encouraging.
"He had a scan yesterday and the news is quite good," said Wenger.
"He will be out for hopefully around a week. He will miss the Sunderland game, but he should be back for next week."
Wenger is facing a headache at centre-back with Mertesacker and Koscielny unavailable for the trip to the Stadium of Light.
Thomas Vermaelen's lack of match sharpness was exposed during Arsenal's heaviest European defeat, while Johan Djourou was far from impressive.
Sebastien Squillaci has been frozen out of the first team picture, but Alex Song can play centre-back if required.
Gervinho has finished international duty at the African Nations Cup and is included in the squad and defender Carl Jenkinson will soon return to training following his back problem.
Wenger also revealed that Kieran Gibbs suffered no setback at the San Siro after being out since October with a groin problem.
"Kieran played his first game in four months in Milan so of course it was a shock to go back to that level. But physically he's all right," said Wenger.
"Carl's back in full training on Monday. That's good news for us."
Djourou has urged Arsenal to atone for last season's Carling Cup final loss to Birmingham by winning the last piece of silverware available to them this season.
"This is a big opportunity for us. The FA Cup is one of the main targets and we have to go for it," he told Arsenal Player.
"Last season's League Cup final defeat is very motivating because we were very disappointed about what happened last time at Wembley and we want to put that right.
"I think it is something still in our heads, and it is difficult to swallow. We know if we can get to the final we can lift the trophy."