McLaren refused to be drawn on whether Jenson Button will be called out of retirement, just six months after he stopped racing in Formula One, to replace Fernando Alonso at next month's Monaco Grand Prix.

Double world champion Alonso, 35, will be absent from the Monte Carlo race after it was revealed he would participate at the blue-riband Indianapolis 500 event instead with McLaren's blessing.

Button, the 2009 world champion, competed in more than 300 grands prix, and spent seven seasons at McLaren. He remains an ambassador for the British team - following a deal struck with former McLaren chairman Ron Dennis last September - and lives in Monaco, too.

The 37-year would appear the obvious candidate to replace Alonso, but whether he, or indeed McLaren, want him to fill the sudden one-off vacancy for the race which takes place on May 28, is unclear.

Indeed Zak Brown, McLaren's American boss who has been integral to ensuring Alonso would be on the starting grid for the Indy 500 in a McLaren-branded car, said they are considering several options.

"Fernando's replacement driver is not in place and those conversations are ongoing," Brown said. "We have a few different options and we will state who that is when we know.

"(Racing director) Eric Boullier, who runs the Formula One team, is ultimately responsible for making the recommendation as to what driver should go in the car."

Button then mischievously tweeted on Wednesday night: "Why do I have so many missed calls?"

Alonso, who raced alongside Button for two years at McLaren, has become increasingly frustrated at the team's failure to contest at the sharp end of the grid.

He is out of contract at the end of the season, but the British team's decision to expand their motor racing portfolio - with the Le Mans 24 Hours race also seemingly now a possibility - could be a sweetener to him staying.

Lewis Hamilton recently appeared to shoot down any chance of Alonso moving to Mercedes, while Daniel Ricciardo and Max Verstappen are under contract at Red Bull until 2018. And although Sebastian Vettel is in the final year of his Ferrari contract, a move back to the Italian team for Alonso is highly improbable.

Alonso insists his future remains in Formula One, but wants to complete motor racing's so-called 'Triple Crown' - that of winning the Monaco Grand Prix (which he has done on two occasions), the Indy 500 and Le Mans 24 Hours - before he retires. Britain's Graham Hill is the only driver ever to have achieved it.

"I consider this Indy 500 as an amazing opportunity for me to take part in this spectacular race and a little step closer to achieving the Triple Crown," Alonso said.

"I do not consider all my future will be in the USA. My driving skills and my technique are developed for Formula One cars and this is what I do, and want to do in the future."

Brown, who replaced the long-serving Dennis as McLaren's day-to-day boss, first floated the idea of Alonso racing at the Indy 500 only last month, before it came to fruition on Monday. Alonso will return for McLaren at the Canadian Grand Prix in June.