The midfielder has joined on-loan from Inter Milan.
He told FC Inter 1908, "I'll still have two years left on my contract after this season.
"Maybe my experience with Inter isn't over yet."
Nainggolan added: “I don't feel hunted. I'm peaceful and calm. I'm going back to Sardinia to do well.
“I made a decision with my heart, I had so many offers: now I want to lift the team in my centenary year."