Chelsea have agreed a €44 million (£36.7m) deal with Ajax to sign Hakim Ziyech this summer.
The 26-year-old, who will be Frank Lampard's first signing since he became Chelsea manager last summer, will move to Stamford Bridge at the end of the season for an initial €40m (£33.3m) fee.
However, the deal could rise to €44m (£36.7m) after add-ons.
Chelsea have confirmed that the move is still subject to personal terms being agreed.
Ziyech impressed Chelsea when he played against them in the Champions League earlier this season as he provided three assists in the 4-4 draw at Stamford Bridge in November.
The Morocco international has been a key figure at Ajax over the past two seasons with 29 goals and 45 assists in 78 games.
The midfielder helped Ajax win the Eredivisie and the Dutch Cup last season and also helped the team reach the semi-finals of the Champions League.
A statement from Ajax read: 'Ajax has reached an agreement with Chelsea FC on the transfer from Hakim Ziyech to the English club.
'The transition is effective from the coming season, as of July 1, 2020.
'The clubs have agreed a transfer fee of € 40 million, which can go up to € 44 million through variables.'
A statement from Chelsea read: 'The move is subject to the player agreeing personal terms and he will remain at the Dutch club for the rest of this season.'