Fernando Alonso will miss this year's Monaco Grand Prix after it was confirmed by McLaren that he will compete at the blue-riband Indianapolis 500 event instead.
Double world champion Alonso, 35, will race in a Honda-powered Andretti car branded as a McLaren.
Alonso's absence for round six of the Formula One championship raises the possibility that Jenson Button, who remains under contract in an ambassadorial role for McLaren, could return for the Monte Carlo race on May 28.
McLaren are yet to reveal who will take Alonso's place.
Alonso is in the final year of his three-season deal with McLaren and has said he will take a decision on his future during the summer break.
— Motor Sport Magazine (@Motor_Sport) April 12, 2017
He has grown frustrated with the performance of McLaren and their beleaguered engine supplier Honda, and there had been some suggestion that he could quit midway through the year.
But, while Alonso will miss Monaco for the Indy 500 - a race considered one of the biggest on the motorsport calendar - the Spaniard insists it will be the only grand prix he will be absent for this season.
"I'm immensely excited that I'll be racing in this year's Indy 500, with McLaren, Honda and Andretti Autosport," Alonso said.
"The Indy 500 is one of the most famous races on the global motorsport calendar, rivalled only by the Le Mans 24 Hours and the Monaco Grand Prix, and it's of course a regret of mine that I won't be able to race at Monaco this year.
"But Monaco will be the only 2017 Grand Prix I'll be missing, and I'll be back in the cockpit of the McLaren-Honda for the Canadian Grand Prix in Montreal in early June."
The Indy 500 forms one third of motor racing's so-called 'Triple Crown', along with the Monaco Grand Prix and sportscars' Le Mans 24 Hours race.
Graham Hill is the only driver to achieve the set, and Alonso, who has won in Monte Carlo on successive occasions in 2006 and 2007 - is keen to emulate the Briton.
"I've never raced an IndyCar car before, and neither have I ever driven on a super-speedway, but I'm confident that I'll get to grips with it fast," Alonso added.
"I realise I'll be on a steep learning curve, but I'll be flying to Indianapolis from Barcelona immediately after the Spanish Grand Prix.
"I've won the Monaco Grand Prix twice, and it's one of my ambitions to win the Triple Crown. It's a tough challenge, but I'm up for it.
"I don't know when I'm going to race at Le Mans, but one day I intend to. I'm only 35 and I've got plenty of time for that."
Alonso's decision to participate in the American race will pave the way for a vacancy alongside Stoffel Vandoorne at McLaren in Monte Carlo.
Button, a veteran of more than 300 grands prix, is under contract with McLaren and could be called upon, while British driver Lando Norris, 19, was signed to the team's young driver programme earlier this year.
McLaren's American boss Zak Brown, who will also be in Indianapolis instead of Monaco, believes Alonso could be in contention for a famous victory.
Brown added: "Could Fernando win this year's Indy 500? Well, I wouldn't be so silly as to make any such rash prediction, but I expect him to be in the mix.
"Put it this way, the team he'll be racing for won the race last year, using the same Honda engine, and he's the best racing driver in the world. That's quite a compelling combination."