The Belgium international joined from PSV Eindhoven for €9.7m.
“I am not afraid of competition,” he told Gazet van Antwerpen.
“Benitez was determined to sign me, he knows my qualities and I will be able to make my mark here.
“There are some great players at Napoli and I’ll try to give my best, just as I did at PSV. It wouldn’t be a problem if I sat on the bench a few times, as I’m sure I won’t lose my place in the Belgium side.”