Everton are aiming to strengthen their defence this summer.
Chelsea have been trying to sign Koulibaly this summer, but have had two bids rejected.
Everton now sense that they may have an opportunity to land the highly-rated defender, and are willing to spend big on him.
Ronald Koeman has made strengthening Everton’s defence one of his main priorities since taking charge at Goodison Park.
The Toffees struggled defensively last season, but Koeman believes Koulibaly’s arrival would help them tighten up at the back.
Everton have well over £100 million to spend this summer, and they are reportedly prepared to invest a sizeable chunk of that money in Koulibaly.
The 25-year-old made 42 appearances for Napoli last season, as he helped the Italian side make it into second place in the Serie A standings.