Milan want to keep Cristian Zapata, but will reportedly ask Villarreal for a discount on the previously agreed €6m fee.
The Colombian international joined the Diavolo in the summer on loan, for €400,000, with an option to buy at the end of the campaign.
The former Udinese man has done enough in 2012-13 to win the faith of Vice-President Adriano Galliani, but the official wants to get the South American in a cut-price switch.
The centre-back, still only 26, has featured in 22 Serie A games and five Champions League ties this season.
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