Alonso is competing in both the WEC and Formula One this season in a bid to become only the second driver, after Britain's Graham Hill, to take the so-called Triple Crown of Motorsport.
That involves the Formula One title, or Monaco Grand Prix which he has also won, the Le Mans 24 Hours sportscar race and the Indianapolis 500. Alonso will race Le Mans in both 2018 and 2019 with Toyota.
The Spaniard entered the Indy 500 last year, leading the race for a while before retiring with engine trouble.
Reporting by Alan Baldwin in London