Alonso committed to Renault for two more years at the end of 2008
Fernando Alonso has warned he could walk away from Formula One if plans to introduce a standard engine for all teams go ahead from 2010.
F1's governing body the FIA has made the engine proposal as one of three options to cut what it views as the sport's excessive costs.
But Renault's double world champion said: "If they approve a single engine that would be the last straw.
"It would be time to start thinking about retirement."
FIA president Max Mosley insists F1 must reduce costs by 2010 to stay credible amid a global financial crisis.
But his proposal to introduce a standard engine has met with disapproval from the road-car manufacturers.
Ferrari threatened to review their participation in the sport arguing; "the use of same engines would deprive F1 of its competition and technological development".
The teams have already agreed to cut the cost of customer engines by more than £12m from 2011 - and are working with the FIA on changes for 2010.
The FIA has given the teams three options to reduce engine costs.
The first is a standard engine produced by a supplier, with current engine makers free to build their own to the same design. The road-car manufacturers in F1 have made it clear they are opposed to this idea.
A second option is for a teams' consortium to obtain a low-cost engine.
And a third, which was initially the idea of the teams, would result in independent teams receiving a complete power-train (engine, gearbox and transmission) for less than 5 million euros (£3.9m) a season.
Alonso's Renault team have made it clear they are opposed to standard engines, but the Spaniard spoke positively about next season's rules changes.
New regulations for 2009 will see the return of slick tyres, the introduction of the new kinetic energy recovery system (Kers) and aerodynamic alterations.
The changes are, in part, designed to make overtaking easier and to increase competitiveness - and Alonso says that will help him in his quest for a third world title.
"The advantage is that practically everybody is starting from zero," said Alonso, who won the Singapore and Japanese Grands Prix last season.
"Next year I will try to be champion. You can't allow yourself to start the championship without thinking you're going to win.
"My objective is to win the title. It's a very clear objective, although it may have to be altered as the year goes on."