Serena Williams and Caroline Wozniacki arrive in New York for World Tennis Day shortly before Maria Sharapova announces failed Australian Open drugs test

Serena Williams and Caroline Wozniacki were among the tennis stars who gathered in New York on Monday on the eve of World Tennis Day - shortly before Maria Sharapova stunned the sport by announcing she failed a drugs test.

Williams and Wozniacki were pictured alongside Gael Monfils and Stan Wawrinka in New York on Monday. 

To mark World Tennis Day on Tuesday, Williams will play Wozniacki at Madison Square Gardens, while Monfils will take on French Open champion Wawrinka.

Serena Williams (left) and Caroline Wozniacki pose for a selfie as they gather on the eve of World Tennis Day

The duo are set to play each other at Madison Square Gardens on Tuesday to mark the occasion 

Stan Wawrinka (left) and Gael Monfils (right) joined Williams and Wozniacki at the event in New York

The four players pose for a picture together at the event on the day before World Tennis Day

Hours later, in Los Angeles, Maria Sharapova stunned tennis by revealed she failed a drugs test 

But while Williams and Wozniacki posed for selfies at Essex House in New York, over on the west coast of the United States, Sharapova was preparing to make an announcement which would shake tennis to its core. 

The 28-year-old Russian called a press conference in Los Angeles to reveal that on January 26, the day she was defeated by Williams in the quarter-final of the Australian Open, she failed a drugs test and meldonium was found in her system.

The substance was banned by the World Anti Doping Agency on January 1, with the organisation having announced its plans to prohibit it on September 29 last year.

Sharapova herself said she received further notification from the International Tennis Federation on December 22, but did not follow the information on the link provided.

The five-time grand slam winner could be banned for up to four years if she is adjudged to have deliberately breached doping regulations.

But the Russian said she had legally taken meldonium since 2006 to help with health issues.

'I had legally been taking this for ten years,' Sharapova said. 'It made me healthy and that is why I continued to take it.

Williams posted a selfie alongside her friend Wozniacki from the gathering on Monday evening

Williams (left) and Wozniacki speak to the audience during the celebration in New York on Monday

The four players are scheduled to play matches in New York on Tuesday for World Tennis Day

Williams and Wozniacki sign autographs for fans during the event at Essex House in New York on Monday

Sharapova (right) failed her drugs test the day she was beaten by Williams at the Australian Open

'I take responsibility for my professionalism in my job and I made a big mistake. 

'I know there will be consequences and I don't want to end my career this way. I really hope I will be given another chance to play tennis again. I can't blame anyone but myself. I have let my fans down.'

Williams and Wozniacki are yet to respond to Sharapova's news, but could give their reaction after their encounter in New York later on Tuesday.