The 23-year-old stopper, who can also play in midfield, has recently been linked with a move to Arsenal after some impressive performances for the Dutch outfit.
Jol is not surprised by the speculation and admits that the Toffees have previously been in for the Belgium international.
"Everton (were interested) but Jan knows he is better with us," Jol told NuSport.
"We have over 4.5million fans. Jan is clever and would only leave the club if he is completely ready for a top European team.
"There were doubts by foreign clubs for a long period on whether he would be quick enough, but that's no longer an issue."
On the Vertonghen speculation and goalkeeper Maarten Stekelenburg being linked to Manchester United, Jol added: "I have received these signals. It's not strange those clubs want them."
Ajax currently sit second in the Dutch Eredivisie and their next game is against NAC Breda on 16th October.
Source: Team Talk
Source: Team Talk