David Moyes hit out at Arthur Masuaku and called his dismissal for spitting "despicable" as West Ham crashed out of the FA Cup to 2013 winners Wigan in the fourth round.
Masuaku is facing a six-game ban after he spat at Latics forward Nick Powell near the touchline at the start of the second half of the Hammers' 2-0 loss at the DW Stadium.
Will Grigg scored twice as Wigan knocked out another Premier League opponent having ousted Bournemouth in the third round.
Masuaku's red card left Moyes seething after the midfielder reacted to Powell challenging him, spitting in his direction while the Wigan player started to walk away.
"Ultimately, Arthur, what he's done, was despicable," Moyes said. "He will deserve everything he gets and he will get something off us as well. It's unacceptable, totally unacceptable.
"The referee [Chris Kavanagh] doesn't see it and can't see it. So it was the players' reaction that got him sent off. Ultimately they got the right decision so I can have no qualms about it."
Spitting carries a mandatory six-game suspension, so Masuaku is now likely to be out until the middle of March.
That will further deplete a Hammers squad that may also be without Pedro Obiang for the foreseeable future after he came off with suspected medial ligament damage.
Moyes was already without eight senior players for this tie and he admitted he was stunned by Masuaku's act.
"I've not seen it from him," he added. "We've given him a game, played him all the time, tried to give him a chance, he wasn't really in the team.
"We like him, he's a really good boy around the club. I've enjoyed him so I'd have to say it is out of character. If you do that then you're going to get the punishment in any walk of life.
"I just asked him, did he spit and he said, 'Yes.' You can't do that anywhere. We'll deal with it appropriately."
West Ham's team featured six changes, as opposed to Wigan's one, and the League One leaders raced out of the blocks and led through Grigg's seventh-minute header.
Moyes had suggested Wigan fans would have traded their 2013 FA Cup triumph for Premier League survival that term but the competition is thought of fondly by Latics supporters and their love affair continued with this win.
It was wrapped up 13 minutes after Masuaku's dismissal through Grigg's second of the game.
His sixth goal in this season's FA Cup was a penalty he stroked beyond Joe Hart after Reece Burke was adjudged to have handled in the box.
"It's been a great day for us as a club when you take on such top-class opposition," said Latics boss Paul Cook. "We played well, great credit to our players. The game had a massive, defining moment. The sending off in the game was huge, in my opinion it altered the course of the game in relation to us, having a more positive effect on us.
"I don't think West Ham could sustain putting us under pressure and the game panned out a certain way."