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.
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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.