He spent 10 years with Vitesse before joining Twente in 2008, where he helped them win the Eredivisie and qualify for the Champions League for the first time in their history.

After being named Dutch Footballer of the Year in 2011,[3] he played a season with Ajax, before returning to Vitesse in August 2012.

In September Janssen broke his shin, he played 10 games total that season, and scored 1 goal.

Janssen's good performance at Vitesse was not unseen, as he received an invitation for the Netherlands national football team for a friendly game against Ecuador on 1 March 2006.

Janssen remained a regular starter for Vitesse in the following season, and was again selected to play for Oranje.

Vitesse trainer Aad de Mos told Janssen he could search for another club, despite an existing contract until 2009.

[6] Moeliker later recovered, but in 2017 it was revealed that he suffered lasting brain damage from the crash, albeit still being able to function and work.

Janssen signed a contract with Ajax for two years and was handed the number 16 shirt, previously worn by Luis Suárez.

Janssen wanted to leave Ajax, after he had heard from Frank de Boer that he would be playing fewer matches in the coming season.