Serena Williams is expected to face Andy Murray in a "Battle of the Sexes" challenge in what began as a Twitter joke, leaving tennis fans wondering who coach and rumored boyfriend Patrick Mouratoglou will root for.

Patrick Mouratoglou frequently tweets about Andy Murray, complimenting his performance in Wimbledon and his overall style in tennis, but is also a staunch supporter of Serena Williams and is speculated to be in a romantic relationship with her.

Williams suggested before she was dethroned as women's champion at Wimbledon that she would be prepared to take on Murray, who proposed Las Vegas as a potential location for any match between them, the Telegraph reports.

It is understood that several venues in Vegas would be interested in ­hosting what would be a re-enactment of two famous male-female tennis showdowns of the 1970s and one in the 1990s, the Telegraph also reports.

But the "Battle of the Sexes" challenge might not be the only competition Patrick Mouratoglou might be split on.

Serena Williams, Maria Sharapova and Victoria Azarenka are all contestants in ESPN's ESPY Award poll to evaluate the best female tennis player, leaving tennis fans wondering who Patrick Mouratoglou will vote for.

Although the French tennis analyst is expected to vote for his trainee, online votes for players remain anonymous and are not publicized by ESPN, so it won't be known who Patrick Mouratoglou will end up voting for.

The ESPY Award is presented annually by ESPN and awards the best players, teams and other sporting-related groups based on popular voting and fan support.