He has denied having an affair but did admit to having "crossed a line," saying he shouldn't have spoken to anyone other than his wife in "any kind of flirtatious manner".
The singer is set to take to the stage for what's believed to be the first time since the allegation came to light, with him expected to perform at a fundraising gig next week.
Maroon 5, which is fronted by Adam, are due to headline a fundraiser called The Event, which will be held the MGM Grand in Las Vegas a week on Saturday (October 1).
The fundraising gala has been organised by The Shaquille O'Neal Foundation, which has partnered with Boys & Girls Clubs and Communities in Schools for the occasion.
The Grammy Award winning band will headline alongside acts including Maren Morris, H.E.R. and Pitbull. The line-up for the event also features comedian John Mulaney.
Do you enjoy reading about celebrities? Sign up for all the best celeb news from the Mirror here .
The allegation of an affair was made by Sumner earlier this month, with the influencer claiming that she had seen Adam for "about a year" and that she was "easily manipulated".
She further alleged that he got back in touch more recently to ask if she'd be comfortable with him naming on of his child Sumner, seemingly in reference to his unborn child.
Adam - whose wife Behati is currently expecting their third child - has denied an affair but said he "used poor judgment" in speaking to anyone other than his wife in a "flirtatious manner".
"I did not have an affair, nevertheless, I crossed the line during a regrettable period of my life," he said in a recent statement. He added: In certain instances, it became inappropriate."
The musician said he has addressed that and taken steps to remedy the issue with his family, adding in his statement: "My wife and my family is all I care about in this world."
Adam said it was the "greatest mistake" he could make but asserted that he takes "full responsibility" and that he will get through the experience with his family.
The Mirror approached Adam's reps for comment.
Do you have a story to sell? Get in touch with us at firstname.lastname@example.org or call us direct 0207 29 33033.