The Spain international had initially been targeted to move to the Emirates stadium in the summer but the transfer was brought forward so the 26-year-old can cover the thigh injury sustained by Kieran Gibbs in Wednesday's draw with Liverpool, as well as the alarming loss of form endured by André Santos over recent months. Monreal has signed a contract until 2017.
The Spaniard, who can operate anywhere up the left flank but is predominantly a defender, has been capped nine times since 2009 and has acted as understudy to Joan Capdevila and, more recently, Jordi Alba. He remains a regular in the reigning world and European champions' squad and had been tracked by Wenger for a considerable period.
"We are delighted that Nacho Monreal has agreed to join us," said Arsenal's manager. "We have been monitoring him for some time now and are really pleased that we've been able to agree this move. 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."
His arrival will effectively mean the end of Santos's Arsenal career. The Brazilian has been exposed as a defensive liability since signing in the summer of 2011 – his substitution at Brighton in the FA Cup fourth round last weekend was greeted with ironic cheers from the away support and boos from the home fans – although he may still be utilised in a more advanced position up the left side if required over the remainder of the campaign.
Monreal, who made his name at his hometown club Osasuna where he progressed through the youth ranks, has represented Spain at youth level, under-21s and with the seniors and made 127 appearances for his first club before moving to Málaga in 2011. He has played 54 times for them since, helping the side to a fourth place finish last season. But, with the club having suffered financial difficulties despite being backed by Qatari owners and having qualified for the Champions League, he came close to joining Athletic Bilbao in the summer and has now been allowed to leave.
Arsenal have raided Málaga before, having secured Santi Cazorla from the club back in August for an initial £12m. Wenger believes Monreal could represent another bargain, despite the fact he is cup-tied in Europe and will be ineligible for the Londoners' Champions League campaign, which resumes against Bayern Munich next month.
Wenger had indicated after his team's 2-2 draw with Liverpool on Wednesday that he would be scouring the market for a left-back to replace Gibbs, who is expected to be absent for at least three weeks with a thigh injury. However, the England international's injury record is patchy and he has previously suffered complications in attempting to return from lay-offs.
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