US superstar Serena Williams says she is ready to play "real tennis" after the enforced rest of coronavirus quarantine.

"I really look forward to getting back on the court," the 23-time Grand Slam champion said in a chat with elder sister Venus during an Instagram live workout on Tuesday (May 12).

"It's what I do best. I absolutely love playing."

Tennis is on hiatus until at least mid-July thanks to the Covid-19 pandemic, with the French Open postponed until autumn and Wimbledon cancelled for the first time since World War II.

Serena said she would come to see the break as "a necessary evil.

"I felt like my body needed it, even though I didn't want it," said the 38-year-old, who last won a Grand Slam title at the 2017 Australian Open.

"And now I'm feeling better than ever. I'm feeling more relaxed, more fit. Now I can go out and play real tennis."

Elder sister Venus, a seven-time Grand Slam winner, began posting workouts on Instagram eight weeks ago and this week she invited Serena, "the greatest tennis player to ever exist - my little sister" to share a yoga-inspired stretching session.

Serena said the exercises, which took about half an hour, served as a warm-up for her, even though they were "a little intense."

"Do not injure yourself doing this," she admonished during one lunge, while advising at another point: "If you have bad knees, like me, use a pad."