Dries Mertens said Napoli must buy new and "top level" players if they want to dethrone Serie A champions Juventus.
Napoli have been linked to Real Madrid midfielder James Rodriguez throughout the transfer window as they look to eclipse back-to-back runners-up finishes.
Colombia star James is wanted by head coach Carlo Ancelotti and Napoli, though a deal with the Spanish giants is yet to be completed.
As the season edges closer, Napoli – who finished 11 points adrift of Juve last term – need to reinforce their squad, according to veteran forward Mertens.
"I just want to say that I see other teams are buying a lot, we've signed Kostas [Manolas]," the 32-year-old Belgium international, who has been linked to the Chinese Super League, said during a Q&A.
"All those we buy must be at the top level and therefore someone like James would be welcome to aim even higher. He could make the difference.
"I think we need to buy great players to raise the level of the team. We already have a strong squad, but if we want to win something, we need to buy in order to raise the level. That is clear."
Napoli have already boosted their defence with the signing of Greece international Manolas from Italian rivals Roma.
Manolas is set to form one of the best centre-back pairings in Serie A alongside Kalidou Koulibaly following his €36 million (£32m/$41m) arrival.
"I found a very good atmosphere and a warm welcome," Manolas said. "I won't tell you the reason I left Roma, as it's personal. The first call I received about Napoli was from my agent, then the director and the coach.
"They made me feel secure about my decision and it was clear straight away that they really wanted me in this team. I never had doubts, that's why I chose Napoli and I am sure I made the right decision.
"I liked watching the way Napoli played and was eager to become a part of it. I'd give anything to win the Scudetto here.
"Carlo Ancelotti is unique for what he's won throughout his career. I promise that I'll do everything I can to help the team achieve their targets and aim as high as possible."