Knol was born in Zevenaar, in the province of Gelderland and started his career at OBW, where he was spotted by Vitesse scouts.
[2] He made his professional debut for Vitesse on 8 September 2000, replacing Theo Janssen in the 80th minute of a 2–2 draw against Willem II.
[8] Starting from the preseason of the 2011–12 season, Knol maintained his fitness at Vitesse while waiting for an attractive offer from abroad.
[10] In July 2012, Knol returned to his former club, Vitesse, initially taking on the role of assistant coach for the under-17 team.
The team, under the leadership of John Lammers and Knol, finished seventeenth, which led to their relegation to the Derde Divisie.