Diorra Marzette-Sanders filed a civil suit in Alameda County Superior Court on Tuesday accusing him of several attacks that left her bloodied, bruised and fearing for her safety.
According to the lawsuit, Marzette-Sanders accused the 6-foot-8, 380-pound Brown of slapping her, hitting her and choking her at different times and threatening to shoot her in the "head before you walk out that door with my son."
"We're aware of it. We're looking into it," Raiders coach Jon Gruden told reporters after Wednesday's practice. "I'm not going to say anything else other than we're aware of it."
An NFL spokesperson told NFL Network Insider Ian Rapoport that the league "will review the matter".
"I am aware that my ex-girlfriend has filed a civil suit against me. I deny the claims. They are false. I believe in the court system where I will clear my name. I will not be making any further comment at this time."
Brown did not practice Wednesday due to a calf strain, per Gruden, who added that Brown was at the facility receiving treatment for the injury.
Marzette-Sanders said the two began dating in March 2017 and had a son together last January. She said the two had a "non-marital partnership agreement'' and she moved around the country to be with Brown before he kicked her out of their home in Texas in June.
Marzette-Sanders is requesting a jury trial and is seeking unspecified compensation, including punitive damages.
The Associated Press contributed to this report