Mulumbu was sent off 12 minutes after coming on as a second-half substitute for an elbow on Rangers midfielder Joey Barton.
The 28-year-old protested his innocence following the dismissal and immediately said he would talk to his the club over lodging an appeal.
“I just jumped higher than Joey Barton,” he said. “I didn’t even know what player it was.
“I just jumped higher than him and I didn’t make any movement with my shoulder. I think it’s harsh but that’s how it is.
“I didn’t make any movement to hurt anybody so we will speak with the coach and the club and see what is the best way to sort this out.”
QPR skipper Barton, who scored Rangers’ fourth goal, also came out in Mulumbu’s defence, saying the aerial challenge ‘did not deserve a straight red card’.
The defeat, the Baggies seventh home reverse of the season, leaves West Brom are seven points clear of the relegation zone.