Arsenal defender Kieran Gibbs has been ruled out for up to six weeks with a thigh strain, according to Arsene Wenger.
The England international limped off during Arsenal's 2-2 draw against Liverpool at the Emirates Stadium on Wednesday, and was replaced by Andre Santos.
The Brazilian endured another difficult game for the Gunners, and Wenger moved last night to strengthen his defensive options, signing Spain international full-back Nacho Monreal from Malaga.
The Spanish left-back could go straight into the team to face Stoke at the weekend, after the Arsenal boss confirmed the club will be without Gibbs for the next four to six weeks.
Speaking at a news conference, and quoted by Reuters, Wenger said: "It will be four to six weeks [out]."
That rules him out of Arsenal's Champions League last-16 tie against Bayern Munich this month.
And Monreal, who featured in the competition for Malaga, is ineligible to play for the Gunners, leaving Andre Santos as the club's only recognised full-back for the fixture - although Thomas Vermaelen can also play the position if necessary.
Wenger's side host Stoke City on Saturday, looking to close the gap between them in sixth place and fourth-placed Tottenham Hotspur.
The Gunners sit four points behind the Champions League places, and face a tough battle to clinch qualification for next year's tournament.
Arsenal have never failed to qualify for the Champions League under Wenger.