Valentino Rossi is to split with chief mechanic Jeremy Burgess, the Australian who has been the Italian's close aide for 14 seasons and helped him win seven world championships in motorcycling's top class.
The Italian told reporters at the season-ending race in Valencia that he would have a new crew chief at Yamaha next season.
"It was a very difficult decision for me because I have a great history with Jeremy. He is not just my chief mechanic. He is like part of my family. My father in racing," said the 34-year-old rider.
"But I've decided for next year I need to change something to try to find new motivation and to have a boost to improve my level, my speed. So this will be my last race together with Jeremy."
Burgess has an unrivalled track record in the sport, having worked with Australian world champions Wayne Gardner and Mick Doohan before teaming up with Rossi.
Rossi, winner of 106 grands prix in all categories, is out of the MotoGP championship reckoning with Spanish team mate and double world champion Jorge Lorenzo fighting compatriot Marc Marquez for the title this weekend.
It is the first time in seven years that the title battle has gone down to the last race.