"I'm leaving football, but I'll put my boots on one last time for you," he said in a video posted on his social media on Sunday night, addressing Slovakia's Marek Hamsik, a former Napoli team-mate who has organised a charity match in early July.
109-time Belgian international Mertens scored 21 goals for the Red Devils and made his last appearance for Belgium in December 2022, during the World Cup in Qatar.
Mertens debuted in football for Eendracht Aalst, whom he joined on loan from Belgian giants KAA Gent. After starting in the Netherlands with now-extinct AGOVV Apeldoorn, Mertens made his name at FC Utrecht (2009-2011) before moving to PSV Eindhoven (2011-2013).
He experienced the best years of his career at Napoli (2013-2022), where he became the club's all-time top scorer with 148 goals in 397 appearances. On June 6th, 2025, Mertens was named an honorary citizen of the city of Naples. Napoli fans gave Mertens the nickname Ciro to give him a more Neapolitan name. Mertens has passed this name down to his son, Ciro Mertens.
He spent the last three seasons at Galatasaray, with whom he won three Turkish Super Lig titles and completed the domestic double in 2025.
Mertens won his first prize with PSV in 2012, when he won the KNVB Beker and Johan Cruyff Shield. Afterwards, he won two Italian Cups with Napoli.