Chris Hughton felt Anthony Knockaert let Brighton and Hove Albion down after the forward's red card left his team exposed to a 5-0 defeat at home to Bournemouth.
The visitors were already two goals to the good at the Amex Stadium thanks to Dan Gosling and Ryan Fraser before Knockaert allowed frustration to get the better of him in the 68th minute.
The Frenchman's scything challenge on Adam Smith left referee Kevin Friend with little option and David Brooks, Callum Wilson and substitute Junior Stanislas were all on hand to pile on further misery.
"I've seen far worse challenges [but] I would accept it's a reckless, emotional challenge," Hughton told a post-match news conference.
"He is aware that he has let the team down."
Brighton lie fourth bottom in the Premier League – five points above 18th placed Cardiff City, who they host in crunch clash on Tuesday.
Knockaert will miss that fixture, along with forthcoming trips to Wolves and Tottenham, with Hughton demanding a reaction from his team-mates as they face up to their Premier League futures being on the line.
"We have to take it on the chin, our worst defeat and worst overall performance," he said.
"There is no doubt they know how poor a performance it was. Everybody will be looking, mostly me, to see the type of reaction from the team."
Bournemouth had only won once since the end of January heading into Saturday's fixture but Eddie Howe was left to reflect upon an emphatic performance that all-but secured his team's top-flight status for next season.
"It's been a difficult run and we know the importance of this win," Howe told reporters.
"Once we got the first goal, I saw a different us. We were more a confident, cohesive unit and it was a much improved second half.
"It's been a frustrating second half of the season after we started the campaign so well. We've been stretched with injuries and it's halted our progress, but we came through it and now we want to finish the season on a high."