Media playback is not supported on this device Vettel joins F1's back-to-back champions

Sebastian Vettel is "unlikely" to break Michael Schumacher's record of seven world titles despite becoming the youngest double champion on Sunday.

That is the view of 1996 world champion Damon Hill, who added that the German's true potential is still unclear.

"Michael's record is very unlikely ever to be beaten," Hill told BBC Sport.

"They changed the rules because he was winning too much. It's much more competitive now than it ever was. Vettel has that to contend with."

Vettel clinched this year's title by finishing third at the Japanese Grand Prix behind McLaren's Jenson Button and Ferrari's Fernando Alonso, the previous youngest double champion. Vettel, at 24 years and 88 days old, beat Alonso's record by 364 days.

Media playback is not supported on this device Champion Vettel salutes Red Bull

But Hill said that although Vettel was likely to continue racing in F1 for more than another decade, he would still find it hard to beat Schumacher's record of seven titles.

"He's already got two in the bag," Hill said. "I would say another four titles in the next 10 seasons wouldn't be out of the question, would it?

"But it's never as straightforward as that. All things were working towards helping Michael come to that level of championships.

"There was a lot of momentum there that created the circumstances. There were objections to the level of winning he was doing, and they changed the sport."

Vettel and his Red Bull team have dominated this season, with Vettel winning nine of the 15 races so far and 12 pole positions - his team-mate Mark Webber is the only other man to qualify at the front of the grid.

Hill said that Vettel needed to be involved in a tougher championship fight against closer competition before he could be definitely judged against the other leading drivers of the day - Alonso, Button and McLaren's Lewis Hamilton.

"You'd perhaps like to see him put through a bit of a tougher test of his mettle - a bit of pressure from another team, a contender," Hill said.

Given the best car on the grid, Vettel not only has grabbed it with both hands and made it work but he's gone to another level Damon Hill 1996 world champion

"It'll come because he's so young. He's obviously going to be driving for a few years yet and there are going to be much tougher times ahead."

Hill said: "He's definitely top drawer," but added: "In F1 you do need some sort of personal rivalry to find out what is going on within each competitor.

"It seems to be that any time there is another driver and the question is, 'which one of these two is better', that spurs them on to push themselves to greater heights.

"It'll come because he's so young. He's obviously going to be driving for a few years yet and there are going to be much tougher times ahead.

"I think Webber has done an amazing job and I think he's an incredibly good driver, but you have to face the fact that Vettel has got the edge on him, so he's not putting the pressure on Vettel that he needs for us to find out exactly what he's made of.

"I wouldn't like to guess what would happen if you put him up against a Hamilton. It might fire Hamilton up. He might need to get some sort of rivalry going.

"Button has shown he's better than we ever thought he was.

"Alonso is the sort of fiery character who you can imagine it being interesting them coming together."

ANDREW BENSON'S BLOG While Vettel is clearly out of the top drawer, it remains the case that, until he goes up against another great in an equal car, his absolute potential is hard to judge Read Andrew's blog here

Hill added that despite Vettel's virtually flawless season, the German had shown signs of the vulnerability in the heat of battle that many observers felt were a flaw last season.

Hill pointed to the last-lap spin by Vettel that handed victory in the Canadian Grand Prix to Button.

"He has cracked under pressure this season," Hill said. "When Jenson was closing in Montreal, he dropped the ball."

But Hill said it was clear Vettel was "exceptional", adding: "One thing that proves that is his age - for a person of his age, coping with all the things that F1 can throw at you apparently with very little difficulty.

"From the moment he put his Toro Rosso on pole and won at Monza (in 2008), that was a sign, a Schumacher moment, where a guy turns up and goes against the form, changes the form.

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"And given the best car on the grid, he not only has grabbed it with both hands and made it work but he's gone to another level.

"That's the point this year, he's begun to go beyond just simply making good use of the best car, he's taking the best car and going into another zone.

"He's done some remarkable things with the best car. His ability to pop a lap in right at the last minute of qualifying and just turn it on when he needs to shows he's got a bit in hand."

BBC F1 co-commentator David Coulthard added: "There's no question he's got all the foundations to establish himself as one of the true greats of the sport. He's in a very elite club of double world champions, back-to-back world champions.