In his capacity as safety advisor to the championship, Capirossi has had cause to sample Yamaha's bike, amongst others, over the course of the season.
Having recently suggested it was impossible for anyone to win with the current Ducati bike, Capirossi has now tipped Rossi to once again be a frontrunner as soon as he gets back on a Yamaha.
Ducati has not won since Malaysia in 2009, when Casey Stoner dominated. Yamaha in contrast has picked up 10 wins and 30 podiums over the past two seasons courtesy of Jorge Lorenzo and Ben Spies.
"I had a chance to do a few laps with the Yamaha in Valencia, and I thank them for it: I realised how competitive it is," Capirossi told Gazzetta dello Sport.
"Valentino is my friend and I think he will be competitive with a winning bike.
"He will regain the enthusiasm, even though beating Dani [Pedrosa] and Jorge is super difficult.
"I think he can win races, [although I] don't know about the title.
"Should he do it, we should all bow to him."