The accusation was made in a court filing in which the defense argued that the woman's sex life should be admissible at Bryant's trial, despite Colorado's rape-shield law.
The defense said the woman had "multiple acts of sex" in the three days before her June 30 encounter with Bryant.
The defense also says two prosecution witnesses had engaged in sex with the woman, and that could affect their credibility, reports CBS News Correspondent Jennifer Miller.
And they say it shows a pattern, with respect to whether the alleged victim consented to have sex with Bryant, reports Miller.
At the heart of the defense attack is a contention that the 19-year-old accuser had a "plan" to have sex with Bryant to attract attention from an ex-boyfriend. Bryant's attorneys say injuries found on the woman could have been caused by sex with someone other than the Los Angeles Lakers guard.
Prosecutors have urged the judge to bar any evidence about the woman's sexual past, saying it is not relevant to whether she was raped.
Bryant, 25, has said he and the resort worker had consensual sex. He faces four years to life in prison or 20 years to life on probation if convicted.
The defense filing was revealed moments after the judge ordered prosecutors to turn over two pairs of underwear belonging to the accuser, a move defense attorneys Hal Haddon and Pamela Mackey say will help them exonerate Bryant by proving the woman had sex with other men around the time of her encounter with the basketball star.
District Judge Terry Ruckriegle said the underwear — worn by the accuser the night of the alleged attack June 30 and the next day when she went to a hospital for an examination — must be turned over to the defense within 24 hours. He chastised prosecutors for balking at a court order to share evidence.
During a closed two-day hearing that began Monday, the accuser is expected to testify for the first time Tuesday, though what she says is expected to be limited.
It will be the first time she and Bryant will be in the same room since the alleged assault at the Vail-area resort.