Rachel Grant alleges Seagal talked dirty to her, pulled down her top, and pushed her on to a bed after she auditioned for a part in Out For A Kill in 2002.
Lawyers for the actor have denied the accusations in US media.
Grant claims she lost the role after she refused his sexual advances in his hotel bedroom in Bulgaria.
Talking to Sky News, she explained she had been flown out to Bulgaria by Seagal and his director, and was invited to run through some lines with them both, before Seagal asked the director to leave the room so he could get to know her.
When it was just the two of them, he poured her a drink, soon began to “talk dirty” to her, and asked her several times to take her top off.
She said: “He asked me to sit on he bed because he wanted to give me a massage.
“I was wearing a top with no straps, so I had my shoulders exposed. I may have joked, but I said no.”
She added that Seagal then went behind her chair and started to massage her shoulders.
The 40-year-old said: “I probably allowed it to happen for a few seconds before I stood up and walked away.
“Because I was in a different position and closer to the bed, he was able somehow to pull my top down.
“It really took me by surprise. I was really embarassed because I was so exposed.”
She added: “It was really awkward. It just got stuck under my breasts and I was so embarassed.
“I was embarassed for him too because it was so awful, what he had done.
“Suddenly this person you are so excited to see and meet becomes this horrible human being.”
As she struggled to pull her top back up, she says he managed to get her on the bed.
Ms Grant, who was 25 at the time of the assault, said: “He didn’t hurt me physically, but he is a big guy and his energy and presence fills the room like you wouldn’t believe.
“I remember turning to the left and right, and saying ‘let’s not do this’.”
As Seagal said she must “want to see his private parts”, she burst into tears and he stopped.
Ms Grant said he apologised, and said “when I work on a film it’s nice to be dating the actress I’m working with, it’s great for on-stage chemistry.
“I even said sorry for not being interested in him.”
The actor said she had blamed herself for wearing a strapless top after the encounter.
She said: “It was such a let down and disappointment because A, I was there for a job and B, I was so excited to meet him.
“That I thought was my mistake, maybe he could see I was excited. It’s no excuse, no one should be brought to meet an actor or producer in a bedroom on their first meeting.”
On leaving the room, she said she could tell the director knew something was wrong, and put his head in his hands as she walked back to her own hotel room.
A few days later Grant received a call from Seagal telling her she was not going to be cast in the film.
She said: “He asked me how I was and he said to me ‘oh Rachel, after looking over everyone, all the actors, we have decided you really don’t fit into the film. On this occasion, we are not going to be able to cast you in the film. We will keep you in mind for other films’.”
Ms Grant had been offered the opportunity to sell the story but did not want people to know about what had happened.
She added: “When all these Me Too stories started emerging, I thought about what happened. I had people messaging me to say I should share the story, but I still wasn’t ready.