Testimony has opened in a defamation lawsuit against Britney Spears' parents, with a top record executive saying he was never told that plaintiff Sam Lutfi was her manager.

Music industry executive Barry Weiss testified in a Los Angeles court on Monday that he was Spears' lifeline during the dark period when erratic behaviour threatened her career.

Weiss testified he never heard of Lutfi before then and only knew him later as someone who made sure Spears was on the set for a music video.

Lutfi claims he was Spears' personal manager and deserves millions of dollars. The defamation case is centered on the way Lutfi is depicted in a book written by Spears' mother about the singer's meltdown.

Weiss said Spears had no manager during that period.