Lewis Hamilton may be confident of winning the world championship this season but two of Formula One's top names are not convinced the British star will take the title.

As practise began for the Belgian Grand Prix at Spa, Robert Kubica of Sauber and Hamilton's former McLaren team-mate, Fernando Alonso, both insisted a Ferrari car will finish on top.

Where they differ is over the identity of the champion-elect; Kubica believing Felipe Massa can claim a maiden F1 title while Alonso is backing Kimi Raikkonen to retain his crown.

With six races to go, Hamilton leads by six points, despite Brazil's Massa racing to his fourth win of the year in Valencia a fortnight ago, while Raikkonen is 13 points adrift in third.

But Kubica feels Massa has the measure of his rivals. The Pole, winner of the Canadian Grand Prix in June, explained: "People don't realise he [Massa] is doing a very good job.

"To trouble Kimi is not easy, but he has done it. Lately, Felipe has more often been in front of him - and with quite considerable gaps.

"He has made massive progress, he is consistent and he has been very quick in both qualifying and the races. He has everything to fight for in the championship, and maybe to win it."

Raikkonen has recently struggled to match Massa's results but twice-champion Alonso, who is now with Renault following a bitter split from McLaren at the end of last year, believes criticism of the Finn is unfounded.

The Spaniard said: "I think Kimi has been a little bit unlucky. I remember in the French Grand Prix he was going to win but he had an exhaust failure. Also there was the accident with Hamilton in the pit lane in Canada.

"There were two or three races where Kimi had the possibility to win, but because of bad luck he didn't manage to take the 10 points. So I think Kimi is still very strong for the championship."

Raikkonen is at the right track to revive his challenge, having won the last three Grands Prix held at Spa. And Hamilton acknowledged the threat posed by the rival who beat him to the championship by one point in 2007.

He said: "There are still a lot of points available, so I don't think it's over for Kimi. For sure, he has his work cut out to catch us up, although Felipe is the closest target for me at the moment.

"I certainly wouldn't say I'm in a comfortable position. You should never feel that. I'm still attacking and I'm still driving for the last race and the end result, not focusing on just winning this race."