Fernando Alonso says it is "impossible" for him to keep chasing the fabled triple crown in the next two years.
This week, the Spaniard is preparing for his third Indy 500 campaign, this time again with a McLaren-linked team.
But next year, he will return to Formula 1 full-time with Renault.
When asked if it is therefore his last chance to add the Indy trophy to his Monaco and Le Mans wins, he answered: "That is a good question.
"I think I am facing this race knowing that in the next two years it will be impossible to come back.
"I would have to miss a F1 qualifying if I wanted to do it and next year I won’t be with McLaren," Alonso said in Indianapolis.
"So for the next few years I will not be here, but we will see what possibilities there are in the future.
"But I don’t want to think about that yet," said Alonso. "I’m concentrating on the coming days."