The double world champion is hoping that his Aston Martin team comes good under the new regulations that will be introduced for next season and suggested that he could bring an end to his long career should he enjoy a successful campaign.
Alonso – who made his F1 debut back in 2001 – told Spanish publication AS: "It depends on the feeling I have next year, how I feel physically and mentally.
"But I don't know. Now I don't have a clear idea. If the car went well, there's a good chance it will be my last year."
The Spanish racer believes it is more likely that Aston Martin tastes success in either 2027 or 2028 and refused to rule out staying with the team for longer if next year doesn't go as well as hoped.
Alonso, 44, said: "I know that I have a better chance of doing well in 2027 or 2028, when there is a stability in the human group that we have now with (designer) Adrian Newey and the others.
"The first year they may do things well, but for the second or third year they are guaranteed to do things well.
"But I have to see it with myself. If the car goes badly, there is a chance that it will continue for another year to end up with a good taste in the mouth. If the car did well, 2026 is likely to be my last year."
Alonso, who won his world titles in 2005 and 2006, added that he won't continue to compete in F1 if he doesn't think his performances are up to scratch.
The 32-time Grand Prix winner said: "(Retirement) will not be due to a lack of competitiveness.
"When I leave Formula 1 I want to leave it as it is now, considering myself the best. And that people from outside, at least 30 or 40 per cent, continue to consider that I am the best.
"I don't want to leave him because I have lost my skills. I'm going to enjoy next year and I'll take it year after year. But yes, I want to leave it on a high."