Carmelo Ezpeleta, head of rights holders Dorna, told BBC Sport: "He thinks he can still win and I am completely sure that he can."
Rossi has won nine world championships in his career
He was won seven premier class titles - at 500cc in 2001 and MotoGP in 2002-05 and 2007 and 2008
He has won 105 GPs in all classes
Only Giacomo Agostini - with 122 - has won more races
Rossi will partner
defending champion Jorge Lorenzo
in the Yamaha team this season, and is hoping to challenge for the title again after two fallow years with Ducati.
Rossi - who won four titles with Yamaha between 2004 and 2009 - managed just three podium finishes in 35 races for the Italian manufacturer but Ezpeleta believes he still has the talent to compete at the very top.
Ezpeleta said: "I'm completely sure he can challenge, with all the talent he has and all the experience he has.
"When he took the decision to go back to Yamaha it was because he wants to come back to the front. He was winning with Yamaha before and he can be at the front again.
"Of course it is good for the sport if he can do it. Valentino is a big name, he is a hero to many and one of the greatest riders in MotoGP history. If he is coming to the podium and winning races it will be very important for the championship."
MotoGP riders try new 2013 bikes
Ezpeleta also backed British rider Cal Crutchlow to continue his impressive form.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.