Napoli president Aurelio De Laurentiis has confirmed Dries Mertens' nine-year stay with the club is officially over after the forward rejected the offer of a new contract.
The Belgium international's previous deal expired at the end of last month, but the Serie A side had been hoping to persuade him to agree fresh terms.
However, De Laurentiis says Mertens was not willing to accept the offer tabled by the club and he is now on the lookout for a new team.
"I feel the love for the club, but I must never forget that football is also an industry as well as pure passion," he told Radio Kiss Kiss.
"Unfortunately, that means sometimes going against what the fans want.
"When a supporter asks me, 'why don't you keep Mertens?' I can only reply that he offered himself to us for another year, because he knows that he's 35 and then has to retire.
"If he makes it a matter of cold, hard cash, then I have to say no. If I have to pay a disproportionate salary to Mertens, that would take money away from next season's budget."
Napoli have already waved goodbye to Lorenzo Insigne, David Ospina, Kalidou Koulibaly and Arkadiusz Milik during this transfer window.
Mertens departs Stadio Diego Armando Maradona, where he arrived in 2013 from PSV, as the club's all-time record scorer with 148 goals.
The 35-year-old scored 11 goals in 30 Serie A outings last season, with his 126 minutes per goal the fourth-best return of any player in Serie A to have netted at least 10 times.
He made 397 appearances for Napoli, placing him behind Insigne (434), Antonio Juliano (505), Giuseppe Bruscolotti (511) and Marek Hamsik (520).
Providing further details on the contract offered to the club legend, De Laurentiis said: "I presented him with €4million per season gross and he refused.
"So I said thank you very much to you, your son Ciro, your wife, for everything you've done here and the extraordinary goals scored, but we cannot go beyond our capabilities.
"I need to have money to buy young players who can represent Napoli in future seasons.
"When we changed all the older players to bring in those like Mertens and Koulibaly, the fans were doubtful, but they became champions here."
