Novak Djokovic of Serbia takes a break from the heat during his US Open Men's Singles match at the USTA Billie Jean King National Tennis Center in New York. Picture: Timothy A Clary/AFP

London - The US Open was accused of sexism on Wednesday after French tennis player Alizé Cornet received an official warning for taking off her top on court to turn it the right way around.

When 28-year-old Cornet returned from a 10-minute heat break in New York she realised her shirt was back-to-front and walked to the back of the court to pull off and adjust her top, briefly exposing her sports bra.

The outfit shift earned her a code violation from umpire Christian Rask who branded her action "unsportsmanlike", saying she had violated the World Tennis Association's rules.

But his decision lead to a volley of complaints about sexist double standards from other players and tennis fans.

Judy Murray, mother of former world number one player Andy Murray, said men changed their shirts on court with no issue.

"Changed at back of court. Got a code violation ... But the men can change their shirts on court," she wrote on Twitter.

"You cannot be serious! Men change their shirts on court all the time ... that's ridiculous!!!!" another fan tweeted.

The US Open has been blasted with temperatures of almost 38 degrees Celsius (100.4°F), with male competitors photographed topless in courtside chairs including Serbian Novak Djokovic.

The row comes amid an ongoing debate about the treatment of women tennis players.

Although women have been paid equal prize money at all four grand slams since 2007, they still lag behind the men on their own year-round tennis circuit.

In 2017, the men's ATP World Tour had prize money of $197.7 million compared with $139 million for the women's WTA Tour.

Last year Cornet, who became known for beating former world number one Serena Williams three times, publicly criticised the ATP which had to apologise for a draw ceremony in which female models revealed groupings with letters hidden under clothing.

"Good job @ATPWorldTour Supposed to be a futurist event right? #backtozero," she wrote on Twitter. 

Thomson Reuters Foundation