Honda's Dani Pedrosa lines up as the early favourite, closely followed by Rossi's team mate and reigning champion Jorge Lorenzo, while Honda new boy Marc Marquez completes a trio of Spanish frontrunners in a new era following the premature retirement of Australian Casey Stoner.
Rossi, a 4/1 shot for the title with British bookmakers William Hill, is their closest rival as fourth favourite with no other rider given better than odds of 40/1 ahead of the season-opener.
The charismatic Italian has ditched his uncompetitive Ducati to return to the Yamaha works fold - the team where he won 46 grands prix and four of his seven world titles in the top category - alongside Lorenzo, but at 34 he is starting to feel the ravages of time.
"My comeback to Yamaha is a great story and a great bet, for me but also for Yamaha," said the Italian, winner of 105 grands prix in all classes, during testing last month.
"Unfortunately I am quite old, this is true, but I feel very good...I hope I can fight again for the podium and to win some races. After that we'll see where we are in the championship ranking."
Rossi and Lorenzo were uneasy team mates in 2010, when the Mallorcan was the young hotshot and won his first title, but the latter is now a double world champion and the atmosphere promises to be much friendlier.
"Probably our relationship is better than three years ago," Lorenzo said at the launch of the YZR-M1 machine last month. "Now we are a bit older, more mature, especially me as I was only 20 when I arrived in MotoGP.
"We do not have to be friends...but if the relationship is good this is much better for us but also for the team. We will try to stay calm and to push together in the same direction."
Pedrosa, runner-up to Lorenzo last season, leads the works Honda line-up following the departure of double champion Stoner and has his best chance yet of a first title after a storming finish to last year with six wins in the closing eight races.
"The team has worked hard to get us in the best place for the start of the season and I'm pleased with my physical situation," the injury-prone rider, now in his eighth MotoGP season with Honda, said in a team preview for Sunday's night race at the Losail desert circuit.
Marquez is 20 but arrives after winning last year's Moto2 title, and the 125cc crown the year before, and even Rossi sees something of his younger self in the Spaniard after impressive times in pre-season testing.
His partnership with Pedrosa and the comparisons with their Italian rival will be one of the leading storylines of the year ahead, with nobody ruling out Marquez taking the title in his debut season.
"If he can stay healthy, he is really going to shake things up this season," said 2006 MotoGP champion Nicky Hayden, who remains with Audi-owned Ducati. "He has been very, very impressive and very fast...he could be a game-changer to MotoGP."
Cal Crutchlow, fastest in Pedrosa's absence on the final day of testing at Jerez with the Tech3 Yamaha team, is aiming to become the first British winner in MotoGP since the late Barry Sheene 32 years ago.
He also has a new team mate in an all-British line-up with Bradley Smith making his debut in the top class.
On the track the big novelty of the 18-race season is the F1-style knockout qualifying format.
The 10 quickest riders from the three free practice sessions will go forward to the second phase of qualifying along with the best two riders from a separate first qualifying that otherwise decides grid places from position 13 downwards.
There is also a new penalty points system for riders who collect regular warnings for endangering others.
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