McLaren allowed Alonso to compete in the famous oval race after it became clear Honda had failed to deliver the team a competitive or reliable engine for the 2017 F1 season. The Spaniard wants to claim motorsport's unofficial triple crown, which includes the Monaco Grand Prix (an event he has won twice) as well as the Indy 500 and Le Mans 24 Hours, which he will make his debut at later this year with Toyota.

His Indy 500 ended 21 laps from the finish when his engine failed. The two-time world champion admits it was hard to return to the F1 paddock after his adventure at Indianapolis.

"Yes, I did think about the possibility of changing series and stopping Formula 1," he said in an interview being published in the next edition of the F1 Racing magazine. "After I did the Indy 500 last year, when I came back there were a couple of races in Austria, Silverstone, when I thought, 'Maybe next year I could try a different series; I could do full commitment to the triple crown and do Indy and Le Mans and maybe that's the best thing'."

Fernando Alonso was a popular addition to the 101st edition of Indianapolis' iconic race. Chris Graythen/Getty Images

Honda's failures at the start of 2017 prompted fears among McLaren bosses that Alonso would quit on the eve of the season, as revealed on the Amazon documentry series 'Grand Prix Driver'. However, Alonso says it was the idea of his career finishing on such a negative note that ultimately dissuaded him from walking away.

"But I felt it was not the time for me to step out -- not right now, not after these results, not with this feeling. I knew I would regret it for the rest of my life and that I would have this bad taste for the rest of my racing career.

"So definitely I still want to succeed. There is unfinished business for me and McLaren together. And I think this year is the time all these things will change. I feel pretty sure about that."