The Sun reports that Tulisa has started proceedings against Justin Edwards, understood to be the man in a six-minute clip featuring Tulisa, which was posted online last week.
The N-Dubz star is seeking damages for breach of confidence and privacy after the video spread across the internet.
A source close to Justin - also known as MC Ultra - told the newspaper: "He feels he can't talk publicly now because of this."
They added: "She's suing for up to £100,000. This latest move by Tulisa has really unnerved and unsettled him.
"It's serious stuff and he's got to take it seriously. It's a lot of pressure for him."
The tabloid reports that Justin denies leaking the video, which was originally being sold for £3.90, or $5.99, on a US adult website.
Speaking out about the tape earlier this month, Tulisa said she was "betrayed" and "heartbroken" by Justin, while X Factor Simon Cowell described whoever leaked the tape as a "scumbag".