Sharri Henry, who claims to be four months pregnant with Northcutt's baby, filed the lawsuit Wednesday in Los Angeles Superior Court.
She accuses Northcutt, a nine-year NFL veteran, of trying to harm her unborn child and permanently disfigure her face May 17 at a Hollywood restaurant.
The cousin is not named in the lawsuit that seeks compensatory and punitive damages.
Jason Lee, a spokesman for the Los Angeles Police Department, would not say whether a police report was filed on the alleged assault.
Messages left with Henry's attorney, Loyst Fletcher, and Northcutt's agent, Walter Jerome Stanley, were not immediately returned Wednesday.
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