MotoGP world champion Nicky Hayden has revealed that his penultimate round clash with team-mate Dani Pedrosa left him with a 'secret' shoulder injury, which he carried to title victory in the Valencia showdown, but which now requires surgery.

Hayden injured his shoulder when Pedrosa lost control of his Repsol Honda and slammed into the side of the American early in the Portuguese Grand Prix, dramatically destroying Nicky's world championship lead in the process.

"Everybody saw my emotions and knew how I felt about Dani when I crashed," Hayden told BBC Sport. "If I'd gone on and lost the title I don't think I could ever have forgiven him. Everybody makes mistakes, but when he took me out I couldn't believe it. All I'd ever wanted to do was be world champion. I knew I had a great opportunity this year and I thought it was slipping away."

Eager to avoid handing Valentino Rossi any further advantage for the Valencia season finale, Hayden deliberately played down the extent of the injury prior to the title decider - in which he sensationally snatched the crown from reigning five-times champion Rossi by finishing in third place, while the Italian crossed the line just 13th after a fall.

"I was carrying the injury in Valencia, but the adrenalin got me through," said Hayden. "I had a good race going until Valentino crashed. I'd fought from sixth and was on [race leader] Troy Bayliss's back tyre. I had nothing to lose. I thought 'win the race or crash'. There was no plan B. But when I saw 'Rossi P18' on my pit board I couldn't believe it. That was the longest race of my life. It seemed like it wasn't going to end."

Because of the shoulder surgery, Hayden will miss the final test of 2006, at Jerez in Spain, from November 28-30.