Napoli's transfer market depends heavily on the future of Koulibaly: should he depart the main target to replace him is Papastathopoulos from Arsenal (sides are set to make a deal) and additionally Senesi from Feyenoord.
If Koulibaly leaves for Manchester City, Napoli would have the economic maneuverability to try to make improvements in other positions, such as Boga of Sassuolo for the attack and Veretout the Roma midfielder to replace Allan.
Sassuolo's asking price for Boga is €40m, and Veretout would require Roma selling a year after making an investment in him.