Valentino Rossi has not ruled out the possibility of making a guest appearance in the World Superbike Championship, but admitted it would not happen this year.

Speculation has been rife in recent weeks that Rossi would ride a Yamaha Italia-prepared R1 during the Qatari round of the World Superbike Championship, possibly against now retired reigning champion Troy Bayliss.

The rumours were sparked after Rossi was quoted as saying the racing in World Superbikes is superior to that of MotoGP.

However, the much anticipated 'showdown' now looks unlikely to go ahead after Rossi, speaking at the launch of the 2009 Yamaha M1, admitted he must concentrate on the defence of his MotoGP title.

Even so, Rossi is still targeting an outing aboard a Superbike at some stage, before hinting that it is still his intention to go head-to-head with Bayliss.

"It was a fun idea, and I would have been very happy," he said. "I would still like to do a race in superbike and I would like to battle with Bayliss, because he is the world champion!

"Unfortunately it is a bit of a difficult period and I didn't have the chance, but I hope that in the future, maybe next year, we can do it."

Ducati boss Davide Tardozzi had earlier told Crash.net that they weren't prepared to enter a third bike for Bayliss, regardless of Rossi's intentions.