De Bruyne returned from his holidays following Belgium's World Cup campaign and linked up with Massimiliano Allegri's squad, but compatriot Lukaku was given extra time off, with the striker set to join the group only once those additional days have elapsed.
Napoli moved quickly to play down any suggestion of a rift, explaining that Lukaku's absence had been agreed with the club in advance of the pre-season camp, though the timing has done little to quiet speculation over his future; the sense within the club is that a sale for around €10m would be preferable to risking losing him for nothing when his contract expires.
Interest has been reported from Saudi Arabia and Turkey, while MLS side Atlanta United have also been credited with interest in taking the Belgian to America before the European window closes. De Bruyne, by contrast, is considered central to Allegri's plans for the season ahead, with the club keen to build a more varied midfield role around him.
Elsewhere, Napoli are considering a third loan move for Eljif Elmas, who is set to leave RB Leipzig this summer despite having two years left on his contract there.
The Macedonia midfielder, who returned to Napoli on loan last season after an earlier spell at Torino, made 44 appearances in all competitions – 33 of them in Serie A, with a goal against Torino among them – and impressed enough to be considered again despite the club previously balking at Leipzig's €17m buy-option when his last loan spell ended; "Napoli will always be with you. Good luck, Elif," the club had posted at the time.
Contacts between the parties have resumed as Napoli explore a second consecutive loan, though Aston Villa and Juventus – whose manager Luciano Spalletti won the Scudetto with Elmas in his Napoli squad in 2023, the midfielder finishing as the side's third-highest scorer with six goals – have also been credited with interest in taking him on should a deal not materialise in Naples.