The Spaniard originally raced for the Woking squad in 2007, joining after winning the drivers' championship two years in a row with Renault.
However after an intense season crowded with controversies, Alonso left the team, only to return eight years later alongside Jenson Button.
His return was not successful, and Alonso walked away from a race seat in F1 at the end of 2018 after three years of fighting in the midfield or towards the back of the field.
He remained an ambassador for the British company, entering the Indianapolis 500 in 2019 with the team - however he shockingly failed to qualify for the race.
At Bahrain, a handful of months before his Indy 500 venture, he drove the McLaren MCL34 during an in-season test.
However, any more commitments to McLaren are not to be expected in the near future, as the 38-year-old has not had his obligations to the team transferred over to 2020.
Alonso is expected to return to Indianapolis later this year to contest the famous 500-mile race once more, with Andretti Autosport being tipped as the team he will enter the event with.
McLaren has partnered up with Schmidt Peterson Motorsports for the 2020 IndyCar season, signing Patricio O'Ward and Oliver Askew as its drivers.
Alonso has indicated that he will decide on a potential F1 comeback in the coming months, while affirming that his priority was the Indy 500.
Any return to the McLaren F1 team is unlikely, as the team has stated multiple times that it is content with its line-up of Carlos Sainz and Lando Norris, who partnered each other for the first time in 2019.
Bahrain International Circuit - Winter testing