Sky Italia says Villarreal have accepted an offer from Milan for Samu, with Carlos Bacca going the other way.
Milan will pay €18m plus Bacca, valuing the player at around €25m.
They will take Samu on loan for €3-4m, with an obligation to buy for €13-14m. The Spaniard is due in Milan for a medical this week.
The Rossoneri see Samu as cover for Suso.