The defender is expected to pen a four-year contract with the Serie A side once all of the formalities of his transfer from Spain have been completed
Villarreal defender Mateo Musacchio is undergoing a medical with AC Milan as he closes in on a move to San Siro.
Milan TV posted footage of the centre-back arriving at La Madonnina clinic and starting his physical tests while wearing club training gear on social media on Monday.
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Reports in Italy suggest the Serie A club have agreed a deal that could eventually be worth €18 million to sign Musacchio and plan to give him a four-year contract.
The 26-year-old has been with Villarreal since 2009, when he signed from River Plate.
Milan finished the 2016-17 Serie A season sixth, meaning they will play in the Europa League next season after three years without qualifying for a continental competition.
Musacchio arrives after playing 23 times in La Liga this season as Villarreal came fifth. He has six caps for Argentina.