Yamaha are concerned they could lose Valentino Rossi to Formula One after the MotoGP world champion clocked good times in tests this week for Ferrari.
"I have to be worried about these excellent times, because Valentino really could get the desire to change sport," Yamaha team manager Davide Brivio told Saturday's La Gazzetta dello Sport.
"The greatest danger is Ferrari (not MotoGP rivals Ducati)." Ferrari have previously tried to recruit Rossi, whose contract with Yamaha expires at the end of this season.
Italian Rossi completed more than 600 km behind the wheel at the Circuit de Catalunya and had a best time of one minute 21.900 seconds, compared to Jenson Button's pole position time of 1:20.527.
