Van der Vaart has compared the German international's style of play to that of a "blind horse”, and insists Chelsea will be better off with Ziyech in the starting lineup.
Ziyech and Werner both arrived in West London before the beginning of this campaign, as part of Chelsea’s attempt to bolster their squad to fight for titles under Frank Lampard.
Ziyech’s deal was completed right after the January transfer window when Chelsea met the asking price of Ajax.
Werner on the other hand was one of the most sought after talents last summer but the Blues beat off competitions from other clubs like Liverpool to secure the services of the German from RB Leipzig.
The Ziyech and Werner are yet to meet their known standards at Stamford Bridge, having combined for 14 goals in all competitions so far.
Van der Vaart wants to see Ziyech play more often at the expense of Werner, insisting the-25-year-old has only pace but lacks skills.
The Dutchman told Ziggo Sport, when asked why he would pick Ziyech for Chelsea and whether it was just because he knows the player from his time at Ajax: "No, it's because he's the best option.
"He is always able to provide for the striker and Giroud needs guys like him. Mount plays in exactly the same way, so that's why I would pick him too.”
"Timo Werner is super fast, and maybe that is something good to have in an away game when Chelsea are under pressure, but all he does is put his head down and run, which leads to nothing.
"Mount is a terrific footballer, and I think he can get even better as he gains some power, but Werner is truly a blind horse. He already shown that's what he's like when he played in Germany - and he's doing it again now."
