Fellaini has been linked with a loan move, but only if the English club pays a percentage of his wages.
"Fellaini is a great player and I know him well," Mertens told Il Mattino.
"I hope he can wear our jersey, but we have to wait and see if he'll come to Napoli or not.
"Napoli want to do better than last season, that is the objective of the team. There are no favourites for the Scudetto this time round.
"I will say Roma had the most active transfer market over the summer and I consider them the most dangerous opponents."
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