According to The New York Times, Danny Kedem, 30, no longer wanted to lead Weiner's campaign after it was revealed that he had continued to have illicit online correspondence with women after leaving Congress.
The move comes as new poll numbers show the married Democrat continues to fall in the polls.
Weiner resigned from the House of Representatives in 2011 after the first batch of lewd photos and texts involving women he had never met in person surfaced.
On Tuesday, Weiner apologized and promised that the "behavior is behind me" after a gossip website printed X-rated excerpts of online conversation Weiner had with a then 22-year-old woman. She has since been identified as Sydney Leathers.
Weiner said he's still "working with people" to get help dealing with his online flirting, but he disputes any suggestion that it's an addiction.
He vowed to stay in the race, saying he believed "people care more about their futures than my past with my wife and my embarrassing things."
His wife Huma Abedin says she will continue to stand by her husband.
No official word has been released from Weiner's campaign regarding Kedem's exit.
The Associated Press contributed to this report.