Sebastian Vettel has stated he does not "understand" why Felipe Massa has struggled so much alongside Fernando Alonso at Ferrari.

The 2012 championship looks set to be a head-to-head contest between Red Bull's Vettel and Ferrari number 1 Alonso.

But with Ferrari still yet to sign up Alonso's teammate Felipe Massa for 2013, German Vettel has revealed some of his feelings about the situation inside the great Italian team.

When asked by Folha de S.Paulo newspaper about Brazilian Massa's lean years between 2010 and 2012, the reigning back to back world champion answered: "I don't understand.

"I really like Felipe as a person and respect him a lot as a driver.

"Many people forget how much he has won and that he lost a title by one point to Lewis (Hamilton).

"Had he been champion, people would talk very differently about him.

"I don't understand why he has suffered so much in recent years," added Vettel.

Massa, of course, has come back from his near-fatal Budapest qualifying crash of 2009, insisting that - physiologically at least - he is just the same as when he went head-to-head for the title against Hamilton.

But also in 2008, Massa was the standout Ferrari driver alongside the then reigning world champion Kimi Raikkonen.

And two years earlier, Massa was regarded as more than a match for his then teammate Michael Schumacher, who was ending his ultra-successful first career on a high.

Vettel said: "With all due respect to Fernando, I think Felipe can be as fast or sometimes even faster than him. But then I don't always understand why the difference between them is so great.

"In the past Felipe has competed with very good drivers like Michael and Kimi and has always been fast, so I don't understand. But I'm not a Ferrari driver and so I don't know how things are there.

"It's just a shame that people forget things so quickly. In 2008 he (Massa) was seen as one of the best and now he's not.

"If his engine had not blown up in Hungary he would be a champion. I know I keep saying 'if', but that's the way it is," Vettel is quoted as saying.