Hailed as one of Saints' brightest young hopefuls when he joined the club from local amateur outfit Blackbrook in July 1998, the Amsterdam-born second row forward has been forced to quit the game following a string of injuries.
Jonkers, a former Cowley High pupil, made his Knowsley Road debut against Salford on March 7, 1999, under Ellery Hanley's stewardship, and the following year scored one of Saints' tries in their 29-16 victory over Wigan in the Old Trafford Grand Final.#

Honours came thick and fast for the 26-year-old who was a member of the successful 2001 squad which lifted the World Club Challenge at the Reebok Stadium, Bolton, where they beat Brisbane Broncos 20-18, and later that year he picked up a Challenge Cup Final winners' after Bradford Bulls had been swept aside 13-6 at Twickenham.

He also featured in the 2001 Grand Final success over Bradford Bulls but after 49 starts for the club and used 73 times as a substitute, he was loaned to Salford City Reds in the 2004 season before making his move permanent.
A reccurence of an injury to his knee forced Jonkers to sit out most of his first season and in March 2006 – with first team chances scarce - he accepted a month's loan deal with Wigan Warrior where he played under his former Knowsley Road mentor Ian Millward.

On his return to the Willows, Leigh Centurions stepped in to take one on loan until the end of the season but further injury thwarted his progress and despite eventually joining the Hilton Park club on a permanent basis and playing eight matches this term, the Irish international has now been forced to hang up his boots.