McLaren boss Zak Brown has all but confirmed Jenson Button will replace Fernando Alonso at the Monaco Grand Prix.
Alonso will not line up on the grid in Monte Carlo on May 28 having opted to race in the Indy500, with McLaren making their return to IndyCar's most prestigious race for the first time in 38 years.
Their car will be run by the Andretti Autosport team, with Alonso keen to complete the triple crown of winning in Monaco, Indianapolis and in the 24 Hours of Le Mans.
Brown had previously said it was not guaranteed Button, who was replaced by Stoffel Vandoorne for the new Formula One season and has intimated he is retired despite taking on the reserve driver role, would fill Alonso's seat in Monaco.
But speaking to BBC Radio 5 Live, Brown said: "When you see our replacement driver, we've got some exciting news. His car is going to run with some guy everybody will be pretty familiar with."
Alonso has made no secret of his disappointment at McLaren's continued struggles with reliability and performance, the Spaniard having failed to finish in Australia and China to start the season.
But Brown denied suggestions allowing Alonso to race in Indianapolis is a ploy to keep him around for the 2018 campaign.
"This is our way of trying to have some success together with our McLaren-Honda relationship. We've agreed to talk about the future in the summer and that's not changed," Brown added.
"I think it will be easy to keep him if we can give him a good race car. It will be difficult if we can't."