Rivals impressed by Massa's form

"Yeah, he is (a threat), but both of them are," said Mercedes-Benz motorsport boss Norberg Haug of Massa and teammate Kimi Raikkonen.

Having outqualified Raikkonen 5-1 this year, and put behind him the nightmares of his first two races, Massa's growing confidence is delivering a run of form that could see him emerge as Lewis Hamilton's main threat for the title.

And on the back of his pole position at bogey track Monaco last weekend, several F1 figures are convinced that Massa is now a much stronger challenger than many expected early on.

Toro Rosso co-owner Gerhard Berger told Autosport: "Massa needs to prove himself this year, and he's doing it race by race. He's always been bloody quick, but he's had some troughs. It seems like he is getting the maximum most of the time now. Impressive."

McLaren F1 CEO Martin Whitmarsh told this week's Autosport: "Massa has always been quick but has not always had the consistency, and not always been error free, but he is doing a fantastic job at the moment and I am sure Kimi is scratching his head on that at the moment."

And four-time world champion Alain Prost is equally praiseworthy of Massa's form - but believes that Kimi Raikkonen's pace may be more about a focus on the title than a lack of ability to respond to his Brazilian teammate.

"Yeah, it's interesting," said Prost when asked about the dynamics between Massa and Raikkonen. "Maybe Kimi has not been very impressive in terms of his performance, and Massa, after he made mistakes at the start of the season, is now very impressive and very fast.

"But Kimi is more stable and seems to be thinking about the championship. I'm not surprised. Kimi is world champion, Massa wants to be world champion, so maybe Kimi does not want to risk going that extra tenth of a second this early in the championship.

"I think since last year he's been one of the contenders. He has speed, and he's now more consistent."