The 30-year-old singer allegedly turned up uninvited at Renner's party, which he was holding at his home to celebrate his milestone birthday.
Renner then ranted about her unexpected behaviour while at Style's Golden Globe party.
According to UsMagazine.com, Renner reportedly told friends: 'Someone comes and tells me she's in my room. I run up and open the door and I'm like: 'Um, hi. What are you doing?'
'She just starts slurring. Her boyfriend [Matthew Rutler] was rubbing her back. Who comes to someone's birthday party that they don't know and gets in their bed?! My parents were there!'
Another source added: 'Christina was a mess at that party. She acted like a fool. Her boyfriend was shushing her and telling her to go to sleep.'
However a rep for the Burlesque star dismissed the claims and said she 'was enjoying herself, but she wasn't in his bed'.