Serena Williams carrying shoulder injury into Australian Open?

Tennis living legend Serena Williams may not be 100% when the Australian Open begins on Monday. 

As Gabriel Fernandez noted for CBS Sports, Williams withdrew from the Yarra Valley Classic, a tuneup tournament happening in Melbourne, because of a shoulder injury. The 39-year-old was set to play a semifinal match versus World No. 1 Ash Barty before she elected to rest for the start of the Australian Open. 

Viewed by many as the greatest tennis player in history and one of the world's all-time great athletes, Williams remains on 23 career Grand Slam titles and one away from tying Margaret Court for the record. The American hadn't competed since an Achilles injury forced her to pull out of the French Open in the second round of that competition last October. 

Williams toppled Danielle Collins 6-2, 4-6, 1-0 (10-6) in the quarterfinal stage of the warmup tournament. 

Per the Agence France-Presse (h/t Yahoo Sports), Williams will face Laura Siegemund (No. 51) in the Australian Open's first round. 

"I feel good. I look at Tom Brady, it's so inspiring," Williams told reporters on Friday ahead of both the Australian Open and the Super Bowl LV matchup between the Tampa Bay Buccaneers and Kansas City Chiefs that will see the 43-year-old Brady make a 10th Super Bowl appearance as he pursues his seventh championship ring. 

"I think with all the new things, all the new technology, all the new physical treatments, rehab, things that you can do ... obviously it prolongs careers for so long."

Williams added she "absolutely wouldn't be playing" if she didn't believe she could again be the top player in the world when in her best form.