Aprilia Racing's Max Biaggi (Photo: Aprilia)

But Rossi would not be drawn on Biaggi's retirement decision saying that for every rider it is a personal choice.

"It is useless for the other riders to speak about his retirement because everyone knows the right moment to stop," Rossi said. "And Biaggi will stop at the top of World Superbikes. He is quite old at 41 so it is a life decision, but I have good memories of great battles together."

For Rossi those memories are no doubt embellished by the fact that he convincingly beat Biaggi both on track, and in the media, in a long running verbal feud.

But soon Rossi will face the same question -- when will be the right time to retire?

Rossi turns 34 next February and has signed a two-year deal with Yamaha to go back and race alongside Lorenzo, another rider with whom he has had an often tense relationship.

The difference is that Lorenzo beat Rossi on the same Yamaha M1 to the 2010 MotoGP championship forcing Rossi to leave for an unhappy two years at Ducati.

And over the past five years, since Lorenzo joined MotoGP in 2008, the Spaniard has a clear advantage in race wins, 26 to 17, over Rossi.

Lorenzo could add to his tally with a win in Sunday's Valencia GP.