[3] Clasie made his professional debut for Excelsior on 15 August 2010, when he was part of the starting line-up in the Rotterdam derby victory against Feyenoord (3–2).

[7] Clasie's creativity was instrumental in Southampton getting to the League Cup final of 2017 where the Saints eventually emerged as runners up.

[14][15] On 22 July 2019, Clasie signed a two-year contract for AZ Alkmaar, leaving Southampton on a free transfer.

He made two appearances in the tournament, coming on as a substitute for Nigel de Jong in the semi-finals against Argentina and started the third place game against the hosts which the Dutch won 3–0 comfortably.

[18] As a combative midfielder with an eye for goal, Clasie's style of play has earned him the label of the "Dutch Xavi".