Ajax boss Eric ten Hag has warned Chelsea that Hakim Ziyech is guilty of being a "trainer's nightmare" at times, but also says that the £36 million ($44m) star's "headstrong" personality is what makes him "brilliant".
Chelsea reached an agreement to sign Ziyech from Ajax on February 24, tying the highly-rated winger down to a five-year contract.
The 27-year-old spent the remainder of the 2019-20 campaign at Johan Cruyff Arena, but will be officially unveiled at Stamford Bridge in July.
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Ziyech has spent the past four years of his career on the books of Ajax, where he has established himself as one of the most effective attacking players in European football.
The Morocco international has scored 48 goals in 165 appearances for the club in total, while also contributing a staggering 82 assists, and played a key role in their league and cup double last term.
He has also been a consistent performer in the Champions League, notably putting in an exceptional display against his new employers during Ajax' 4-4 draw away to Chelsea in this season's group stages.
Ziyech will be expected to work the same magic at the Bridge while wearing the home colours, but Ten Hag has advised Chelsea to "give him space" on the training pitch in order to bring the best out of a mercurial figure.
The Dutch head coach told Ajax TV after Ziyech's final training session with the club: "Hakim is 'what you see is what you get'. You see what his emotions are doing to him today.
"He said 'I am not a man of club love, but at Ajax it is different'. It is an emotional day for Hakim, but [I hope] he looks back on it in a good way.
"He comes in as a big man at Chelsea, a top club in Europe. That is the example for the younger players here. First become the best here, win titles and then take the step.
"He is a character, headstrong. But that also makes him brilliant.
"He sees things that others don't see. Sometimes he is a trainer's nightmare, but you have to give him space.
"If they start playing on their responsibility, you see the development. He took Ajax by the hand and we were very successful together."