The singer's ex-manager filed the suit in 2009, alleging libel, defamation, battery, intentional infliction of emotional distress and breach of contract.
Her former nanny Lourdes Torres is being lined up as a witness for Lutfi's case, which relates to statements made about him in Britney's mother Lynne's book Through The Storm, A Real Story Of Fame And Family In A Tabloid World.
"Lulu is going to be called as a witness by Sam Lutfi's lawyer to testify about what she witnessed when she was a nanny to Britney's two children, in the months after the conservatorship was put in place in 2008," a source told Radar.
"Lulu will testify that she believes Britney was being emotionally manipulated in the conservatorship and will blow the lid off of what was really going on with her. Lulu ended up quitting her job because she was so disturbed by what she saw was happening to Britney.
"Lulu signed a non-disclosure agreement so she has never been able to go public with her concerns for Britney. However, the NDA doesn't cover a court of law and Lulu is ready to testify.
"Lulu's testimony could have significant impact on the jury because she spent a great deal of time with Britney and her parents after the conservatorship was put in place. Lulu isn't after money, she just wants the truth to come out and it will be shocking."
The trial is expected to last three weeks, with Lutfi, Lynne and Jamie Spears and Britney's fiancé Jason Trawick all scheduled to testify. The judge who oversees Britney's conservatorship has already ruled that she is not fit to give evidence.
However, Lutfi's lawyer is "still pushing the judge handling the lawsuit" to call Spears as a witness.