McLaren the main threat, says Alonso

"I think both. McLaren for sure because they have the Michelin tyres, they will improve the car a lot and they will be extremely competitive," said Alonso ahead of the San Marino Grand Prix.

"I don't know from which point of the championship but we are all sure at one point of the championship they will make a good step forward with the car and from then they will be competitive.

"And Ferrari is a little bit more of a doubt because it depends on the tyres, how they work and how quick they are. Probably Ferrari will be a little bit more up and down. Some circuits they will be good, some of them they will be bad, depending on the tyres.

"But for sure McLaren will be there at the end of the championship fighting."

At the same time, Alonso believes the Honda team, tipped as one of the favourites to fight at the top before the start of the season, will not fight for the title and he admitted he would be surprised if Jenson Button manages to win a race this year.

"I think they will be quick and they were quick also in the three races, they had three first rows in qualifying, so compared to last year they improved a lot and they are fighting for podiums and that is good news," he said.

"To fight for victory I think they need a couple of tenths and a little more luck.

"The championship I think will be a bit more difficult. They need three years on top to fight for the championship. If they win this year it will be a surprise."

In a similar situation to last year, Alonso and his Renault team have stolen the early march over their rivals in the first three races of the season. The Spanish driver holds a 14-point gap over his own teammate Giancarlo Fisichella and McLaren's Kimi Raikkonen.

And like last season Alonso believes consistency, and not only wins, will be key to retain the crown.

"At the moment I think we are really strong, package, and we have no mechanical problems so we finish normally all the races with no problems and we score points," Alonso said.

"Once you have a little bit of an advantage in the championship and you finish all the races then it doesn't matter if it is third or fourth it is difficult (for others) to recover their advantage.

"So if we keep constant and we try to finish on the podium, as we did last year, in the second half of the championship, then it will be difficult to reach our points. But it is too early to say, probably."