 After being named Dutch Footballer of the Year in 2011, he played a season with Ajax, before returning to Vitesse in August 2012.Janssen began his career at amateur club Vitesse Arnhem 1892 and played from 1995–1996 in the reserves of SBV Vitesse.After breaking through in several youth teams Janssen made his professional debut on 9 December 1998 in the first team against NAC Breda, which Vitesse won 2–0.