Donald Trump claimed in a tweet that Hillary Clinton “can’t satisfy her husband”.
It is the latest insult directed at Mrs Clinton since she announced she was running for US president next year.
Property tycoon Trump removed the message after he was accused of sexism.
It read: “If Hillary Clinton can’t satisfy her husband what makes her think she can satisfy America?”
The April 16 tweet referred to the affair Mrs Clinton’s husband Bill had with White House intern Monica Lewinsky in 1998 when he was President.
Trump, host of the US version of The Apprentice, has not apologised for the tweet. A spokesman claimed it was retweeted by one of his staff and as soon as Trump saw it he deleted it.