The Congolese midfielder picked up the ball and kicked it at Gary O'Neil after being fouled in the final minutes of Saturday's match at Upton Park.
Mulumbu will now serve a three-match ban and miss the upcoming fixtures against Arsenal, Newcastle and Southampton and used his Twitter account to express his regret over the incident.
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West Brom goalkeeper Ben Foster, however, sent the 26-year-old a message of support and insisted that the sending off was out of character.
"Don't u worry about it mate, you're Mr Professional, everyone slips up some times," he posted on his own account.
The Black Country club's head coach, Steve Clarke, admitted that Mulumbu had let his frustrations get the better of him on a disappointing day in east London.
"I think Youssouf thought he had been clipped and he overreacted," he told the club's official website.
"After the game, I said to the group in general that they have to control their frustrations. It was a frustrating afternoon for us. We chased the game for most of it.
"We also had some chances but you could feel the frustration building because we didn't get the game back to 2-1 to give ourselves a chance of getting something from it. But you have to control yourself.
"The red card didn't affect the game today because it happened so late but it will affect the group for the next three games. We've got a small squad and Youssouf will be a big loss to us."