McLaren CEO Zak Brown must be barking mad to allow Fernando Alonso to race in the Indianapolis 500, says Red Bull team principal Christian Horner.
Alonso is set to miss the Monaco Grand Prix next month in order to take part in IndyCar's most prestigious event, which McLaren are featuring in for the first time in 38 years, their car being run by the Andretti Autosport team.
The two-time Formula One champion has made no secret of his disappointment with McLaren's ongoing struggles, the Spaniard having failed to finish each of the opening two races of the season.
He is also keen to follow in Graham Hill's footsteps and become only the second man to win the Monaco GP, the Indy500 and the 24 Hours of Le Mans, motor racing's Triple Crown.
But Horner has questioned McLaren's decision with Alonso having no previous experience of IndyCar, saying: "It's a difficult one for Fernando, he's having a tough time.
"[McLaren CEO] Zak [Brown]'s got the problem of a depressed driver on his hands and he's trying to keep him motivated and come up with this idea to send him to Indianapolis.
"He must be barking mad, it's the nuttiest race I've ever seen!
"No testing, he's going to just jump in the car... turn one is a proper turn, it's easy flat the whole way round. I think he needs to see a psychiatrist, personally!"
Jenson Button will make a one-race return to fill Alonso's seat in Monte Carlo, but Horner cannot foresee him allowing one of the Red Bull drivers to do the same as Alonso.
"Would we let our drivers do it? No," Horner said. "I think if a driver commits to a team it's like disappearing with another girlfriend half way through the year, doesn't seem like the right thing to do.
"Perhaps if the races didn't clash, or do it at the end of his Formula One career... but McLaren have got this approach which is perhaps different to ours, but good for them."
Brown responded on Twitter by posting a picture of Horner jumping into a pool in what can best described as questionable clothing, captioning the tweet: "Er... sorry Christian, which of us needs to see a psychiatrist?!"