Serena Williams has long taken advantage of the licence for players to express themselves through their clothing at the Australian Open and on Tuesday she was at it again during her first-round match against Germany’s Tatjana Maria.

The 23-time Grand Slam champion warmed up on Rod Laver Arena in a long, black raincoat which she discarded to reveal a figure-hugging, bottle green one-piece costume paired with fish-net compression stockings.

"It's a Serena-tard," the 37-year-old later told a news conference to laughter, adding that she thought it "an incredibly strong, powerful statement for moms that are trying to get back and get fit".

While the Australian and U S Opens take a laissez-faire attitude to what players wear, Wimbledon has a very strict dress code and the French Open will be ramping up their restrictions after Williams wore a black spandex catsuit last year.

French Tennis Federation president Bernard Giudicelli told Tennis Magazine last August that the catsuit was a step "too far" and that players would be expected to "respect" the tournament in the future.

For Williams, the catsuit, she said, made her feel like a "superhero", and the compression stockings she will wear for the duration of the tournament at Melbourne Park, have a more serious purpose.

The American has previously spoken about health concerns over blood clots and the possibility of suffering Deep Vein Thrombosis since she had her daughter by Caesarean section in September 2017.

"Definitely still concerned," she said on Tuesday. "I have had some issues, and they're not done. So it's just something I just have to do for pretty much probably the rest of my career, we'll see. But I'm always at the doctor.

"With DVT, it's very scary. A lot of people have them. Especially for me it's incredibly frightening. I lay on the side of precaution as opposed to not."

Returning to the Australian Open for the first time since winning it in 2017 while pregnant with her daughter, Williams on Tuesday made short work of Maria, who was wearing a more conventional black and lilac outfit.