Koulibaly seemed to confirm that Sarri would be the next Chelsea coach before any official announcement was made, and spoke highly of the Italian.
Koulibaly signed for Napoli in 2014 from Belgian side Genk and has become one of the best, and most sought-after, defenders in world football after four impressive seasons in Serie A.
The Blues are in a spot of bother over the future of Willian, who has been heavily linked with a move to Manchester United.
Senegal and Japan fans help clean up stadiums following World Cup games
Even if you're not insane about sports, the World Cup often brings out the best stories of compassion and worldwide peace. But Africa is full of quality and we're on the way. "But we fully trust our football, we have no hang-ups".
That's where he plays for Belgium, on the opposite flank to Eden Hazard.
His exploits over the last couple of seasons also make him a possible option as the focal point of attack, potentially making him an attractive short-term solution.
Mertens had a £24.5 million release clause in his contract which expired last week and Napoli will surely demand a high fee from a club which will be interested in his services.
But Chelsea deemed the 31-year-old too old and too expensive. On the other hand, Chelsea still have Conte on their payroll.
It now remains to be seen if Sarri is able to convince the Chelsea board to sign Mertens and kick-start their transfer spending for the summer.