"I was going to say something extremely rough to Hillary, to her family and I said to myself 'I can't do it. I just can't do it. It's inappropriate. It's not nice,'" Trump said during the debate.
He later told NBC News that he held back on making those comments because Chelsea Clinton was in the room.
Trump lashed out after Hillary Clinton pointed to misogynistic comments the New York businessman has made in the past.
"[Trump] tried to switch from looks to stamina, but this is a man who has called women pigs, slobs and dogs, someone who has said pregnancy is an inconvenience to employers, who has said women don't deserve equal pay unless they do as good a job as men," said Clinton, the Democratic nominee, while Trump attempted to deny her statements.
Trump acknowledged that he has said "very tough things" to Rosie O'Donnell, but said he thinks "everybody would agree that she deserves it and nobody feels sorry for her."
Trump has previously called O'Donnell "crude, rude, obnoxious and dumb" and a "loser."
— NBC News' Hallie Jackson contributed to this report.