Mundo Deportivo says Villarreal are set to sign Marin on-loan for the remainder of the season.
The Spaniard joined Napoli in the summer from Real Madrid, with the deal including a buy-back option.
It's understood Real are happy with the prospect of Marin returning to LaLiga and to Villarreal.
Real still see Marin as a potential future player and management believe the move will be good for his development.