With the prospect of playing Andre Santos desperately close, Arsenal pulled off a last-minute deal for Spain international Ognacio 'Nacho' Monreal from Malaga.
The Gunners agreed a fee believed to be in the region of £8.5 million ($13.5 million), with the 26-year-old signing a long-term contract.
"Arsenal Football Club is delighted to announce that Spanish international defender Nacho Monreal has agreed to join the Gunners on a long-term contract for an undisclosed fee," the club said in a statement on their website.
"The deal is subject to the completion of formal registration processes."
Arsenal's need for a left-back was dire after it became clear that Kieran Gibbs would miss the next three weeks because of a thigh strain picked up during the team's 2-2 draw with Liverpool.
Gibbs' replacement Santos endured another horrible outing after coming on for the England international, and has seen his stock go down alarmingly this season, with mistake after mistake being committed whenever he has been given an opportunity.
Arsene Wenger admitted he would look to bring in a left-back before the window shut Thursday, and the Arsenal manager has pulled off a coup in bringing in Monreal, who was thought to be a summer target for next season.
"We are delighted that Nacho Monreal has agreed to join us," Wenger told the club's official website. "We have been monitoring him for some time now and are really pleased that we've been able to agree this move today (Thursday).
"Monreal is a strong left-sided defender with good experience at both club and international level. He is a technically gifted player, a good crosser in the final third and strong in the air.
"Monreal will add quality to our squad and of course, to our defensive unit. We all look forward to him playing for us."
Monreal, who is unfortunately cup-tied in the Champions League, has earned nine international caps for Spain up to now and is seen as the understudy to Jordi Alba of Barcelona.
The defender joined Malaga only in the summer of 2011 from Osasuna, and now joins up with former teammate Santi Cazorla at Arsenal.
