He was also under investigation recently, following an allegation of a serious breach of discipline, believed to be related to a drinking session.
Rovers utility back Wayne Ulugia was also released by Rovers recently for similar disciplinary reasons.
Walker leaving follows hard on the heels of the sacking of head coach Craig Sandercock.
A club statement reads:
“Hull Kingston Rovers have agreed to release prop forward Jonny Walker from his contract with immediate effect in his pursuit of regular first team football elsewhere.
“The club would like to wish Jonny all the best for the future.”