Singer Gifty, who is in the Girls category, was caught swearing on camera after her pal Sam Lavery made it through the public vote.
As Sam's name was called out, Gifty turned to her and said: "I f***ing knew it!"
Once all the safe contestants were confirmed, host Dermot O'Leary was forced to apologise to viewers. He said: "You may have just heard some inappropriate language, we deeply apologise. As you can imagine, tensions are running high."
Following the broadcast of the ITV1 show, a handful of viewers complained to Ofcom. A spokesman later told The Sun: "We've had five complaints about this. We will assess these complaints before deciding whether to investigate or not."
Gifty later shared 12 'crying with laughter' emojis on Twitter after fans pointed out her potty mouth, adding: "I didn't even notice I did it!"
Gifty was among those who made it through Sunday's live shows, with Ryan Lawrie, Four Of Diamonds and Relley C finding themselves in the bottom three. Ryan was saved by the public flash vote, while Four Of Diamonds were saved following a sing-off with Relley.
Speaking on This Morning following her exit, Relley admitted she was "gutted" to leave the competition, especially after being struck down with a cold last week.
"We are only human and we do get sick. I was just disappointed I had to get sick at that stage of the competition as I would have loved to have gone ever further but nevertheless I've had the best time of my life," she said.