Double world champion Fernando Alonso said on Tuesday he would think about quitting Formula One if the sport adopted a standard engine from 2010.
"If they approved that, it would be the last straw. It would be time to think about retirement," the Spaniard told reporters at a charity event organised by his Renault team's sponsors ING.
Formula One's governing body, the International Automobile Federation (FIA), said in October it intends to change the rules to force teams to use a standard engine from 2010 as part of a cost-cutting drive.
It has since launched a tender for bids to provide the engine, although it said this is only one of three options being considered.
Champions Ferrari, who could well figure in Alonso's future, and Toyota have already said they will consider pulling out if standard engines are imposed.
Alonso, champion with Renault in 2005 and 2006, said Formula One is going backwards technically with recent regulation changes.
"In 2005 we had a V10 engine with 1,000 horsepower," he said. "That was what was exciting for the driver, motor racing at the limit.
"We have gone from the futuristic to cars without grip or electronic aids which look like something from the past."
Alonso won two races for Renault this year with the French manufacturer recovering from early doldrums to end the year in fourth place overall.
In 2009, with the introduction of slick tyres and the new KERS device that recovers energy from the brakes to provide extra bursts of power, the Spaniard said he would be going for the title again.
"I cannot allow myself to start the championship without thinking I am going to win," he said. "My aim and that of the team is the title. It's a very clear objective, even if as the year progresses one may have to adapt to circumstances."