Valentino Rossi could choose to retire from MotoGP at the end of the year if new team-mate Yamaha Maverick Vinales "hands him his arse", 500cc legend Kevin Schwantz feels.
Switching from Suzuki to Yamaha for 2017, Vinales topped all four winter tests, and went on to dominate first practice for the Qatar Grand Prix on Thursday, lapping nearly 1.5 seconds quicker than Rossi.
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The Italian, who had a subdued pre-season by comparison, said he was struggling to feel comfortable on Michelin's 2017 tyres after the session.
Rossi signed a fresh two-year contract with Yamaha in Qatar 12 months ago, covering the 2017 and '18 seasons.
By the end of 2018, Rossi will be nearly 40 years old, but he has left the door open to continuing beyond this current contract.
However, Schwantz believes that if Rossi consistently lags behind Vinales this season, his plans could change as he has other career objectives to fulfill outside of MotoGP.
"Rossi is saying he wants to drive Le Mans [24 Hours], and do all the other things not yet on his list of accomplishments," the 1993 500c champion told Autosport.
"He's kind of preparing himself for it.
"Do I think he'll retire at the end of the year if Maverick hands him his arse weekend in, weekend out? He possibly could.
"He's got other things to keep him occupied, like his Moto3 team, the ranch going on, trying to get in racecars.
"So he could pretty easily walk away from the sport.
"I'd like to see him hang on another year or two, but it's hard to sleep at night in those circumstances, thinking, 'my team-mate has two or three tenths a lap on me, every lap.'
"It makes for long weekends and, as competitive as Valentino is, he wants to be in the mix every weekend.
"If he is not consistently in there for the first half of the season, I think we may see him make his career change."
Schwantz does, though, feel Rossi will finish in the top three of this year's championship, also tipping Vinales to beat reigning champion Marc Marquez to the title.
"The good thing from [Rossi's] point of view is that if the Marquez vs Vinales battle gets to a stage where they're taking each other to the ragged edge, falling off, screwing each other around, there could be a place for a 'Mr. Consistent' to pick up the pieces," he said.
"He can keep himself in championship contention that way."