According to Sky Sport Italia, the negotiations are at a very advanced stage and personal terms agreed with agent Jorge Mendes.
The 31-year-old Portuguese international would arrive on a six-month loan with option to make the move permanent at the end of the season.
Postiga’s current contract with Valencia runs until June 2015.
He would be a replacement for Sergio Floccari, who is on the verge of joining Sassuolo.
Postiga only joined Valencia from Real Zaragoza in August for €3m, scoring four goals in 23 competitive games for the club this season.
The forward has also played for Sporting Lisbon, Porto, Panathinaikos, Saint-Etienne and Tottenham.