Ziyech will join the Blues on July 1 for a fee rising to €44m. The midfielder was signed in February.
In a video tribute, several former and current teammates congratulated the midfielder on the switch.
Eintracht Frankfurt wing-back Jetro Willems, who was this season on-loan with Newcastle United, laughed: “If you just tell the trainer that you have stomach flu against us. Then everything will be alright!"
Juventus defender Matthijs de Ligt stated: "I'm sure you're going to show it in the Premier League and you're doing well. I wish you success."
Barcelona midfielder Frenkie de Jong also remarked: “Congratulations on your transfer to Chelsea, well deserved! Both as a player and a person you are really a winner. Just stay who you are, then you will also make it there."