Former Ajax coach Aad de Mos believes Chelsea will be the biggest test in their Champions League group.
Ajax have drawn Chelsea, Valencia and Lille for their Champions League group.
De Mos told NOS: "Ajax is the best team of the four.
I think Ajax will continue with Chelsea. Valencia started the season weakly. They only have one point and are no longer the team of last year. They have many problems with the owner.
"Lille is a good team, but they have lost their top scorer to Arsenal (Nicols Pp).
It is a fantastic draw. We get six beautiful matches. And for the fans it is interesting to go to those beautiful cities."
