Maverick Vinales did not appear on track during Friday morning's opening practice session for the Malaysian Moto3 Grand Prix at Sepang - and has now quit the Avintia Blusens team.
During the session it was rumoured that the Spaniard, who recently re-signed with Avintia for a further year of Moto3 and then a move to Moto2, had refused to ride.
Vinales later announced that he will not race for the remainder of 2012.
"Since halfway through the season, they [the team] haven't done all they could, I'm always giving my best - so I wanted to leave the team after the last three races [of the year] and have a clean break-up, but they wouldn't agree so I'm heading home today," the official MotoGP website quotes Vinales as saying.
Despite signing the contract extension until the end of 2014, Vinales claimed that Avintia is "a second division team", adding: "I have to try and win the championship next year and I don't think I could do it with this team, so that's why I took this decision."
Vinales has won five races this season - more than any other rider - and is second in the World Championship standings, albeit 56 points behind KTM's Sandro Cortese with three rounds to go.
Cortese and team-mate Danny Kent are both leaving the Red Bull KTM team for Moto2 next year. Luis Salom has been signed, but the other factory KTM seat is not yet occupied and they would surely be interested in Vinales.
Vinales - who is now set to lose second in the championship to Salom - has frequently called for more engine performance from his FTR Honda to counter the KTMs this year.
When asked about his contractual situation with Avintia, Vinales said: "You can sign whatever you want, but when things just get worse and worse, you have to find solutions."
Vinales' motorcycle broke down on the warm-up lap in Aragon, but the Spanish teenager has also made mistakes of his own, notably crashing out of the victory fight on the final lap in Indianapolis.
Avintia team manager Ricard Jové stated that Vinales' decision came out of the blue.