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Chelsea are still negotiating with Victor Osimhen on the exact make-up of his potential wage package.
The multi-layered nature of the transfer means the move, which also involves Romelu Lukaku going to Napoli, could run until the last week of the window.
There also remains the possibility that the deal could be a loan with an option to buy.
As it stands, the two clubs are close to agreement on a mutually beneficial deal that would see big-name strikers trade places.
Napoli cannot afford Osimhen's huge wages, which were partially agreed as part of a new deal to secure a higher fee this summer.
Chelsea are one of the few clubs this summer who are willing to spend on a prime No.9 who also has commercial appeal, so they are more than willing to take the Nigerian.
That may well prove convenient, too, since they have long wanted to offload Lukaku and new Napoli manager Antonio Conte sees the Belgian as his ideal forward after working with him in the past.
While almost everything is agreed on the Lukaku side, Osimhen and his camp are holding out for the €12m net they feel they should receive from Napoli.
Chelsea are willing to be flexible from their otherwise rigid wage structure for a "star" such as the 25-year-old, knowing that is also required to amplify the commercial appeal of the club.
That is partly why the talks are so protracted, though, due to what are described as "complex" negotiations about how to structure his pay.
Chelsea's approach to such contracts has evolved in the time while Clearlake Capital have been majority owners, and the make-up of deals are said to be more multi-layered than rival clauses.
A deal like Osimhen's would involve all manner of conditionals, as well as clauses and bonuses related to image rights.
While there remains a feeling in the market a deal will get done, there is still a lot to be concluded.
The current expectation is that Lukaku will go to Napoli permanently and Osimhen will initially be a loan.