Red Bull team chief Christian Horner described his McLaren counterpart Zak Brown as "barking mad" on Friday for agreeing to allow Fernando Alonso to miss the Monaco Grand Prix and race in the Indianapolis 500.
Sitting alongside the American at a scheduled news conference for team principals ahead of this weekend's Bahrain Grand Prix, Horner launched a savage appraisal of his rivals' decision.
"It is a difficult one for Fernando as he is having a tough time," said Horner.
"And Zak has this problem. He has a depressed driver on his hands and he is trying to keep him motivated.
"He has come up with this idea to send him to Indianapolis, but he must be barking mad. It is the nuttiest race I have ever seen.
"No testing. He is just going to jump in the car. Turn One is a proper turn as well -- it is not easy flat all the way around. So, personally, I think he needs to see a psychiatrist."
Horner said he would not have allowed any of his drivers to leave the team during a season to race in another series.
"I believe if a driver commits to a team, it's a bit like disappearing with another girlfriend halfway through the year and then coming back.
"It doesn't seem to be the right thing to be doing.
"Perhaps if the races didn't clash -- or do it at the end of his F1 career, but, obviously, McLaren have got this approach, which is perhaps different to ours. But, hey, good for them."
Brown said he backed Alonso to rise ro the challenge of the famed Indy 500.
"Fernando's not scared. It's obviously going to be a challenge but he wants a challenge," said Brown.
"He'll have a car capable of running at the front. He'll be extremely prepared and I think he's going to put on a good show. Everybody is going to be watching."
McLaren's decision to let Alonso go to Indianapolis was widely greeted as a welcome breath of fresh air by many others in the paddock before Horner's outburst.
Alonso will be replaced at the Monaco Grand Prix by 2009 world champion Jenson Button, the team confirmed on Friday morning.