The couple were spotted together at London's M restaurant on Friday night following the actor's fight which was filmed for his upcoming TV show Idris Elba: Fighter.
The star is in training for his latest TV show
According to The Daily Mail, Idris, 44, and Madonna, 58, made "no attempt to hide" their affection for each other during a party at the establishment.
"There was nothing subtle about it, no attempt to hide. It was very blatant," the source revealed.
"They were at the party for about an hour, they would dance, go off to smooch, then mingle a bit more. They only had eyes for each other. That seemed very clear."
The Like a Prayer singer also shared snaps and videos of Idris on her Instagram and Snapchat, revealing that she had also attended his boxing match, captioning the clip: "Idris Elba Smashes it at York Hall!"
The couple originally met on Madonna's Rebel Heart tour
She also shared a snap of herself lying on the floor with the actor, writing: "I kicked his butt".
However hours after the rumours began, Idris denied that he was romantically involved with the singer. Taking to Twitter he warned fans: "Don't believe the hype."
The pair met for the first time back in 2015 after he DJ'd for her Rebel Heart tour. Opening up about meeting her while promoting Luther, the actor said: "I was excited, I had a great time. Madonna is a legend. I got there, I met a beautiful person that has been working for ever and ever, amen, and is still going.
"She did an incredible show. I was standing by the curtain before I went on and I made the mistake of peeking to see who was there, thinking maybe they’re not here yet, and then I saw there were actually 17,000 people looking back… and then I ended up going out there to entertain them. [But] they weren't there to see me."