Fernando Alonso says his future in Formula 1 beyond 2017 will depend on how much fun he has driving next year's cars, admitting he may quit the sport if they are not challenging enough.
The two-time champion has been in Formula 1 since 2001, and has a contract with McLaren until the end of next season.
New regulations will come into play in 2017 to make the cars faster and harder to drive, and Alonso admits his continued presence on the grid beyond then will be determined by how much fun he has.
The Spaniard has often been critical of the current generation of cars, stating that they are too slow.
"The cars are slower than a few years ago - the feeling is that we have to save fuel, tyres, batteries... there's a constant saving that goes against the instinct of a driver, which is pushing to the maximum," Alonso told Spanish radio COPE.
"So my continuity in Formula 1 will depend on next year's rules, as the cars will be very different.
"If the cars are fun, if you have the feeling that you are driving on the limit as it has always been the case in Formula 1 in the past, it won't be a problem for me to stay.
"If this saving formula continues, then we'll see."
Alonso insisted that McLaren's performance will not affect his decision, as long as he enjoys the driving.
"My contract with McLaren ends next year and I'll think about it. But it has nothing to do with the results, it's more about how much I enjoy it behind the wheel."
Despite the McLaren-Honda partnership not having achieved the results it had hoped for so far, Alonso says he is still relishing the challenge.
He said: "During these tough two years and with a project that started from zero, I'm having fun and I'm learning a lot of things.
"Growing with McLaren and Honda together from zero and hopefully until we succeed is a huge challenge for a driver's career.
"If I felt like I had to win races or if I didn't have any titles I would feel a different pressure or would be more impatient to win, but in my case it's a wonderful challenge in which I'm involved."
Additional reporting by Jose Carlos de Celis