Tony Barretto, 28, appeared as the much-hyped secret witness in the case between the troubled pop princess and her ex-husband Kevin Federline.
Barretto was prepared to testify “on issues of nudity by Ms Spears, drug use, and safety issues involving the children post-rehab,” his lawyer Gloria Allred said outside court.
But Family Court Commissioner Scott Gordon held only a brief open session before clearing the courtroom of everyone but lawyers for Spears and Federline, 29, to privately discuss unsealing documents in the ongoing case.
Mr Barretto worked for Ms Spears from March, when she left rehab, until May 17, Ms Allred said outside Superior Court in Los Angeles yesterday.
The singer married Mr Federline, known as rapper K-Fed, in October 2004, but filed for divorce last November, which became official on July 30.
The two currently have joint custody of sons Sean Preston, 2, and 1-year-old Jayden James.
But citing the 25-year-old’s erratic behaviour, including late nights out with the children, K-Fed is fighting for a 70-30 split in child-rearing duties and for more money, according to US reports.
The appearance of Mr Barretto, described by his lawyer as a “key and secret witness,” came on the day that Ms Spears’ manager and lawyer both quit.
Lawyer Laura Wasser, who represented Ms Spears until yesterday, said Mr Barretto was a disgruntled employee.
She said Ms Spears will be in “excellent hands” with her new lawyers and added: “I don’t want anyone to perceive that we’re dumping Britney.”
Later, Ms Spears was dropped by her management company, The Firm, just a month after she hired them for the run-up to the release of her new album on November 13.
In a statement, the company said: “We believe Britney is enormously talented, and has made a terrific record. But current circumstances have prevented us from properly doing our job. We wish Britney the best.”