Victory over QPR came at a cost for Arsenal.
Arsene Wenger revealed Thomas Vermaelen had to be replaced by Francis Coquelin in the 54th minute through injury.
"He had a calf strain so maybe at midnight I will try to find a left-back," he said with a smile.
"It is serious enough not to play on Monday [at Fulham] or against Leeds.
"We have three left-backs out but Coquelin came out in this position and did quite well, but of course he is a central midfielder."