The pop star is said to have turned up at the actor's 40th birthday party uninvited and got so drunk she started "slurring" and laid down in his bed.
A source overheard the 'Mission: Impossible - Ghost Protocol' star say: "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."
According to the insider, Jeremy continued to say that he was shocked to find Christina's boyfriend Matthew Rutler in his bedroom with her and questioned what the couple were doing there.
He reportedly said: "Her boyfriend 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 told Us magazine: "Christina was a mess at that party. She acted like a fool. Her boyfriend was shushing her and telling her to go to sleep."
A representative for Jeremy confirmed the 30-year-old 'Burlesque' singer was at the party, held on Sunday (16.01.11) - but said she, " was enjoying herself, but she wasn't in his bed."