The Nigerian international has impressed at the Serie A club on loan.
Now it appears the 22-year-old will be joining Walter Mazzarri’s side permanently.
The full back is signing for £8.7 million, per Goal.com.
Aina is one of many Chelsea players who typically go out on loan every season.
But the club is looking to trim its roster, meaning many of these players will be sold.
The list includes the likes of Tiemoue Bakayoko, Tomas Kalas, Mario Pasalic and Danilo Pantic.