Clasie was brought into the first-team squad at Feyenoord at the start of the 2011–12 season and incoming coach Ronald Koeman immediately handed the youngster a place in the starting line-up. On 31 July 2011, he made his debut for Feyenoord in a friendly game against Málaga. Because of his good play and his tenacity he soon became one of the most popular players among the supporters. On 29 August2014, a day after Clasie helped Feyenoord qualify for the group stage of the UEFA Europa League, Clasie agreed to extend his contract until 2018. Clasie explained the decision that he was keen on developing himself as a player within the team as well as developing together with the team as a whole.
However, on 15 July 2015, Clasie signed for Southampton on a five-year deal for a fee in the region of £8 million. This meant he would once again link up with Ronald Koeman who brought him into the Feyenoord first-team. In the summer of 2016, Frenchman Claude Puel took over at the helm of Southampton. Clasie then scored his first goal for the club on 30 November 2016, in a 2–0 win over Arsenal in the EFL Cup. Clasie's creativity was instrumental in Southampton getting to the League Cup final of 2017 where the Saints eventually emerged as runners up. He scored his first Premier League goal on 8 April 2017 in a 1–0 victory at West Bromwich Albion.
On 30 August 2017, Clasie joined Club Brugge on loan for the duration of the 2017–18 season.
Feyenoord
On 25 July 2018, the midfielder rejoined Feyenoord on loan for the duration of the 2018–19 season.
AZ Alkmaar
On 22 July 2019, Clasie signed a two-year contract for AZ Alkmaar, leaving Southampton on a free transfer.
International career
In November 2010, two months after his debut for Excelsior, he was selected for the Netherlands U21 squad. In February 2012, Bert van Marwijk, the coach of the first team of the Netherlands, pronounced his interest in Clasie. He was made aware that his name was on the stand-by list for Euro 2012. Clasie was part of Louis van Gaal's 23-man squad for the 2014 FIFA World Cup in Brazil where the Dutch finished third beating the likes of defending champions Spain and hosts Brazil. 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.
Playing style
As a combative midfielder with an eye for goal, Clasie's style of play has earned him the label of the "Dutch Xavi".
