Still recovering from knee surgery, Van Ginkel was on-loan with PSV Eindhoven last season.
He told De Telegraaf: "With the boys who can make a difference, such as Dusan Tadic, Hakim Ziyech and Donny van de Beek, who often scores in Champions League matches - Chelsea has to watch out for those three.
"But collectively Ajax is good and in the back it is also fine. Although I do not know if it is as good as last year.
"I have been in the Netherlands for the past ten days, not at the club. And Chelsea has a larger team of analysts than we are used to in the Netherlands. So they really have a good idea of Ajax and know how or what to do."