Fernando Alonso has confirmed he will race in the Indy 500 next year, but has left the door open on a return to Formula One in 2021.

The 38-year-old, a two-time F1 world champion, intends to return to Indianapolis as he once again tries to become just the second man after Graham Hill to win motorsport's triple crown of Le Mans, F1's Monaco Grand Prix and the Indy 500.

Alonso first won in Monaco in 2006 and has added two Le Mans victories over the past two years, along with the World Endurance Championship and the Daytona 24 Hours Classic.

However, success at the Indy 500 has provided elusive, with Alonso leading through 27 laps in 2017 but retiring 24 laps from the end due to engine failure.

"I will definitely do Indy. Let's see how the next weeks unfold," he told BBC Sport.

"Indy is the only one missing. If I do that after winning Le Mans, WEC, Daytona, there is nothing more I could ask. Definitely I will try again."

Fin de semana de F1!! Estaré en Monza ayudando en todo lo q pueda a mi equipo @McLarenF1 . Ganas de volver a pisar uno de mis circuitos favoritos, un podio mágico! Especialmente con las victorias de 2007 y 2010. Compartirlo con los equipos y el público es increíble! Buen finde pic.twitter.com/VG7UuKHXTK
— Fernando Alonso (@alo_oficial) September 5, 2019

Beyond that, Alonso admitted he could return to F1.

A world champion in 2005 and 2006, Alonso has not raced in the sport since the 2018 season but a comeback in 2021 is possible should he decide he is missing the thrill of F1 racing.

"First I want to do Dakar and Indy and then see if I'm missing F1," he added.

"This year, it was nice to be out of the F1 bubble but my friends are saying, 'Now you are out of F1 it is the time to enjoy life a bit'. And I say that what makes me happy is to race.

"F1 is still a possibility. The 2021 rules are quite interesting. Maybe it will move things around a bit and make the cars easier to race. If it turns out I miss F1, I am open to coming back.

"Also the driver market is very open for 2021, so there is no hurry to make a decision."