An investigation by LBC claims Ian Byrne, who is running for Liverpool West Derby, shared a message in 2015 about Baroness Michelle Mone, the founder of underwear brand Ultimo, which called to “hit the c*** where it hurts.”
On Thursday night during a speech in Manchester, the Labour leader said: "I am very proud of the work done by all my colleagues, some of whom are behind me here today.
"And I'm very proud of all the work that is going into our manifesto for this election."
Mr Byrne’s post, shared in 2015, received comments calling for violence against Baroness Mone, and accused her of betraying her working-class roots.
He also commented on a post about housing minister Esther McVey, who was at risk of losing her seat, calling her a ‘b*****d… and soon to be gone’.
Mr Byrne’s Facebook account has been deleted.
A statement from Mr Byrne today read: "I am deeply sorry for the inappropriate and offensive language from the shop floor that I used several years ago on social media and would not use today.
"I also shared a meme about a Conservative peer who voted to take away tax credits from the poorest and most vulnerable people.
“The person who originally posted the meme had used an unacceptable and misogynist language to describe her. This was not my language and I sincerely apologise.
"I'm a very different person now and I'm grateful that the labour and trade union movement has enabled me and so many other working class people to represent and fight for our communities.
“Through setting up Fans Supporting Foodbanks, I've been working to overcome divisions and bring our Liverpool community together and if I'm elected that's what I will continue to do, transforming our communities in the interests of the many, not the elite few."
Yahoo News UK has contacted the Labour Party for comment.