Arsenal's physios have given Thomas Vermaelen an anti-inflammatory injection, hoping he can be match fit for the Champions League second round tie against Bayern Munich a week on Wednesday.
The Belgian defender has already had a similar injection this season on his injured ankle, which forced him out of Saturday's win over Sunderland.
He will return to light training this week.
The club has a worryingly long injury list, with defenders Laurent Koscielny and Kieran Gibbs both out. And Carl Jenkinson added to Arsene Wenger's defensive worries, incurring a one-match ban for a second yellow card in Saturday's match.
But those worries weren't enough to make Wenger keep hold of left-back Andre Santos, who arrived in Brazil over the weekend to finalise his loan move to Gremio.
And long-term injury worry Jack Wilshere should be fit for the Bayern game after a thigh injury sustained at the Stadium of Light left no lasting damage.
He could even play in Saturday's FA Cup clash with Blackburn, but Wenger may consider resting him.
Wenger was angered by the attention Sunderland paid the 21-year-old, who recently spent 17 months on the sidelines with an injury, and he said referee Anthony Taylor should have done more to protect his prized midfielder.
He said: "It was frustrating because Jack Wilshere didn't get the free-kick he deserved. But it is a question, I hope, of him taking four or five days to recover.
"From very early he was handicapped. It is down to the referees to protect him when it is needed."