Lewis Hamilton believes he could have severely damaged his career if he had leaped into F1 as Jaime Alguersuari will do this weekend.

Alguersuari will become the most inexperienced rookie to race a F1 car in Sunday's Hungarian Grand Prix as he has done nothing more than two straight line aerodynamic tests for Toro Rosso.

At 19 years 126 days, Alguersuari will certainly be the youngest to compete at the sport's highest level, a decision by the team that could seriously backfire.

Prior to signing his deal with McLaren ahead of the 2007 season, there was talk of Hamilton racing for the team in the final three races of 2006.

But it never materialised as it was realised Hamilton's inexperience counted against him, with the reigning world champion appreciating he "wouldn't have been ready."

"All I can say is any driver in the world would jump at the chance to be in a F1 car," said an understanding Hamilton of Alguersuari's position.

"I can't look at it and say 'I wouldn't do it' because I would have done it, just the same, but fortunately I had people around me when I did come in.

"In 2006, when (Juan Pablo) Montoya left (McLaren), I was going to replace him at China, Japan and Brazil, and I'd only done straight line tests, but it would have been the worst move of my career.

"It took me eight days of strong, core testing before I felt really comfortable in the car and matching the pace of Pedro (de la Rosa) and starting to compete with the other guys.

"It takes confidence and a lot of preparation. If I hadn't have had that testing and I'd gone into China, who knows if I'd have got my drive the following year.

"For me, it wasn't a good idea, but he may prove us all wrong, and all the best to him."

Current championship leader Jenson Button is "surprised" the young Spaniard has been allowed to race this weekend bearing in mind he has not even turned a corner of a circuit in a F1 car.

Although Button was only 20 when he made his debut, he at least had a winter's worth of testing behind him.

"You've got to say good luck to him, and it's a risk he's obviously willing to take. For his sake I hope he does a good job," said the 29-year-old Brawn GP star.

"It's not just about driving quick. There's a lot more to it. I'm sure he does not understand a Formula One car, or the electronics.

"To start with, the steering wheel is very complicated, and trying to get the pit stops sorted in two days is going to be difficult."

Expressing his serious concerns, Button added: "At his age it could absolutely destroy his career. It could end his dream of being competitive in Formula One."

Defending himself, Alguersuari said: "I'm relaxed.

"I know what I can do, what people can expect from me, and the most important thing is I know what I have to do.

"It's another car, another race in my career. At the end it's just one steering wheel and two pedals."