Sebastian Vettel is having to come to terms with the realisation that his world championship challenge to Jenson Button has almost certainly gone up in smoke.

Earlier in the season Vettel, the 22-year-old German dubbed the 'new Schumacher', looked like posing the greatest threat to Button after winning the Chinese and British Grands Prix.

But his hopes of eroding some of Button's lead in the title chase were dashed in Valenica at the weekend when one Renault engine suffered a spectacular blow-up in qualifying and its replacement failed during the race.

As he headed to this Sunday's Belgian Grand Prix at Spa, now trailing Button by 25 points, Vettel was making all the right noises. "As long as the championship is possible, I will fight until my last breath." he said. But Red Bull boss Christian Horner conceded that Vettel will almost certainly exceed the maximum permitted supply of eight engines this season, and that will mean a race-ruining 10-place grid penalty every time he uses an extra one.

Horner is aware that two of the toughest tracks on engines, Spa and Monza, which hosts next month's Italian Grand Prix, are still to come. He said: "Since Silverstone the momentum has been very much with us, reducing the points lead of Button and Brawn GP.

"But we've had four engines failures with Vettel and it is almost inevitable that we will have an engine penalty somewhere, which is very frustrating. We will just need to manage that and think strategically for the right time to take that penalty."

A rule limiting each driver to eight engines was introduced this season in a bid to help cut the exorbitant cost of competing in Formula One. The idea, along with a strictly-policed maximum limit of 18,000rpm, was to shift the emphasis from outright performance to reliability.

It has worked for most drivers, with more cars than ever finishing races. Vettel, who in Spain signed a new long-term contract with Red Bull, has just hit an unlucky streak. One consequence over the remaining six championship rounds will be a team-imposed restriction on the number of laps he undertakes in practice, starting with Friday's two sessions at Spa.

By keeping practice mileage down, Red Bull will hope their engines will be fresher for the race. But Vettel acknowledged: "The more laps in practice you do, the more experience you get, the better you understand your car, and the better you can set it up for qualifying and for the race."

Renault have issued an apology to Red Bull and Vettel over the failures. Fabrice Lom, who heads the French company's engine support programme, said: "I can assure them that we will work as hard as possible to ensure it doesn't happen again."

But he added: "The end of the season will now be tough on the engine side for Sebastian."

Brawn, meanwhile, believe that Rubens Barrichello could pip team-mate Button to the title. Barrichello triumphed in Spain and Brawn GP chief executive Nick Fry said: "We're in a position now where both drivers have proven they can win, Rubens has shown what he can do and Jenson's won six, so I wouldn't bet against either of them."