The footage of Clive Lewis was reportedly taken at an event held by the pro-Jeremy Corbyn hard-Left Momentum group at the Labour conference in Brighton.
Former shadow business secretary Mr Lewis is heard to say: “Get on your knees, b****.”
It was unclear whether the words were aimed at a woman, but a Momentum source claims it was a man kneeling on stage taking score during a “game show segment” at the event.
Norwich South MP Mr Lewis, once tipped as a future Labour leader, said: “I apologise unreservedly for the language I used at an event in Brighton last month. It was offensive and unacceptable.”
However, he was quickly attacked by top female Labour MPs at a time when women politicians have received a high level of abuse on social media.
Ex-deputy party leader Harriet Harman said on Twitter: “Inexplicable. Inexcusable. Dismayed.”
Women’s parliamentary Labour Party chairwoman Jess Phillips said she was “appalled” and former minister Yvette Cooper tweeted: “No excuse for saying this, whatever context.”
A party spokeswoman said Mr Lewis’s language was “completely unacceptable and falls far short of the standard we expect of Labour MPs”.