Tennis sisters Venus and Serena Williams were sued for allegedly backing out of a match against John and Patrick McEnroe that was to be billed "Battle of the Sexes II."

The suit, by a non-operating Web site called Women's Sports Zone, estimated potential profits from the exhibition at $45 million. The company couldn't get started without those funds, its attorney, Abbey Kaplan, said Monday.

The suit, filed Thursday in Palm Beach Circuit Court, accused the sisters and their father, Richard, of breach of contract. It said Richard Williams acted as his daughters' agent and signed a contract for the match. The match was agreed to but never was scheduled, Kaplan said.

The suit does not specify damages.

Keven Davis, a New York attorney for the sisters, said they never authorized the deal with Women's Sports Zone.

"They know they're wrong, and we're going to have to prove it in court, unfortunately," he said.

Miami lawyer Guy Robinson, who is representing Richard Williams, had no comment.

Women's Sports Zone still exists but is not in operation, Kaplan said. It has no telephone listing in Palm Beach County.

"Battle of the Sexes" was a 1973 exhibition match in which Billie Jean King beat Bobby Riggs.