MILAN, Jan. 28 (Xinhua) -- AC Milan completed its winter purchase on Friday when they signed left-back Didac Vila from Spanish side Espanyol.

The transfer fee is believed to be 4 million euros with the defender accepting a four and a half years deal. A statement on Milan's official site read:

"A left-back was the last missing piece of an excellent transfer campaign carried out by the Rossoneri management. The mission has been completed as 21-year-old Didac Vila Rossello has joined Milan from R.C.D. Espanyol de Barcelona.

"Once again, Adriano Galliani's personal intervention proved to be decisive, as the Milan CEO left for Barcelona immediately after the presentation of Van Bommel and Emanuelson to return to Italy with the Spanish starlet, who's seen as the final piece to complete the Rossoneri defence."

Vila made his debut for Espanyol on 29 January 2009 and has since cemented a place in the first team and becomes Milan's fourth January signing after Antonio Cassano, Mark van Bommel and Urby Emanuelson.