Napoli are looking ahead to next season and Arkadiusz MIlik could be heading off in a transfer as Osimhen becomes an idea to join. There could be a piece brought back in the deal for the striker if he departs, which is likely as he will not extend his contract with Napoli. The price for Milik is high however, and a purely cash offer cannot be counted on. Napoli rather are asking for a player back in exchange: that could be Bernardeschi from Juventus or Lucas Moura from Tottenham.
Both players can serve as wingers rather than at striker, a position that is covered by Mertens, Petagna, and possibly Osimhen. Napoli will have an open posiiton there when Callejon departs.