Yamaha boss Davide Brivio has apologised to Valentino Rossi for the Japanese manufacturers' poor 2007 MotoGP season.
Yamaha were no match for rivals Ducati for most of the season, and the Italian marque's rider Casey Stoner dominated the championship with 10 victories.
Rossi, who only needed one point in the season finale at Valencia to secure the runner-up spot, went on to finish in third place in the championship after retiring with a mechanical problem from Sunday's race.
The Italian's exit, together with Honda's Dani Pedrosa victory, left the seven-time champion in his worst championship position since 1997.
Rossi, who raced with a broken hand at Valencia following a crash on Saturday, was furious with Yamaha after the race.
Brivio apologised to the Italian and admitted the team will have to work hard during the winter.
"We must apologize to Valentino," Brivio told Gazzetta dello Sport. "Throughout the season we have always analyzed the season in a clear-headed way.
"It's obvious that in 2007 we've had problems with the performance of the engine and tyres. All of this can, in fact must, become a stimulus for our engineers.
"During the year we were unable to quickly improve the performance of the engine. We have a big job to do at home during the winter.
"To have Valentino Rossi in the team puts enormous pressure on us, and to support him we must put the maximum effort in. We did not hide behind Michelin problems, even when we could have done so."