West Ham manager David Moyes has called Arthur Masuaku's sending off for spitting "despicable" and vowed to punish his player.
The midfielder saw red in the 49th minute when he spat at Latics forward Nick Powell near the side of the pitch, as the Hammers were dumped out of the FA Cup 2-0 at Wigan.
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 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."
Victorious boss Paul Cook, a boyhood Liverpool fan, said of the fifth-round draw: "We need one hot ball and one cold. Liverpool at Anfield and we can settle for that."
He added: "It's been a great day for us as a club when you take on such top-class opposition.
"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."