Dean Harrison has been released from his Mar-Train Racing contract with immediate effect.
The Bradford racer had been due to ride for the Northern Ireland team in 2016 but has left Tim Martin's outfit to take up a new challenge.
Harrison helped lead the development of Yamaha's new YZF-R1 Superbike in the manufacturer's official road racing team this season but has opted not to fulfil the second year of his two-year contract in 2016.
Team principal Tim Martin said: “Dean has been instrumental in getting the new R1M to where it is now and has been a pleasure to work with over the past two years.
“He is a talented young rider and needs to follow his own aspirations, I wish him all the best and would have no hesitation in working with him again in the future.
“Hopefully we will be in a position to confirm our 2016 plans in the next week but our commitment to Yamaha UK and the YZF-R1M project remains intact, we made a lot of progress throughout 2015 and are looking forward to reaping the benefits with a successful 2016.”
Yamaha UK's Motorsport Co-ordinator, Karl Radley, added: Taking a brand new bike road racing is always going to be a steep learning curve, but Dean kept pushing and delivered some fantastic results on the new R1M, for which Yamaha is very grateful.
“Dean's commitment and work ethic has been rock solid throughout the season and whenever the chips were down, he has always bounced back and remained utterly professional.
“We understand and accept his decision and I would like to thank him both personally and on behalf of Yamaha UK and wish him the very best for the future.”