West Ham United manager David Moyes described Arthur Masuaku's actions as "despicable" after the defender was shown a straight red card for spitting at Wigan Athletic midfielder Nick Powell in their FA Cup defeat on Saturday.
Wigan pulled off the big shock of the fourth round as the team from the third-tier of English football knocked out the Premier League side with striker Will Grigg's double sealing a famous 2-0 victory.
West Ham were reduced to 10 men after Masuaku was sent off soon after the break for spitting.
"It was despicable," Moyes said after the game. "I've not seen it from him. We like him, he's a really good boy around the club... it is out of character."
"He will deserve everything he gets and he'll get something he deserves from us. It's unacceptable."
West Ham, who are 11th in the league, take on 13th-placed Crystal Palace on Tuesday.