Alonso has 10 years to win Le Mans

Webber, who returned to sportscar racing with Porsche after his Formula 1 career at the age of 37, suggested that time was on Alonso's side in his bid to become only the second driver to win the Monaco Grand Prix, the Indy 500 and Le Mans.

"He can do it in the next 10 years, there's no rush," said Webber, who took the 2015 FIA World Endurance Championship title before retiring at the end of last season.

"The Indy 500 in his eyes is the harder one to get, and I would probably agree with him. He can take time to get Indy and then the opportunity has to be there to win Le Mans, which can also take a while."

Porsche and Toyota, the two manufacturers involved in the LMP1 division in the WEC, have both dismissed the chance of Alonso joining them for Le Mans next year.

Webber said he has no doubts that his friend, who is racing a Honda-powered Dallara for the Andretti team in this year's Indy 500 on May 28, has the potential to become only the second driver after Graham Hill to complete the triple crown.

"His skill is not in question; I believe, yes, he can win both races – he has the hunger and the mindset," he continued. Hats off to him for giving it a go."

Webber revealed that Alonso had joked with him about also racing at Indy this year, but said that he had never had any interest in competing in the Indy 500 during his career.