Serena Williams pulled out of the Yarra Valley Classic with a shoulder problem after reaching the semi-finals of the Australian Open warm-up event.

The 23-time grand slam champion did not mention that anything was amiss after defeating Danielle Collins 6-2 4-6 10-6 in the quarter-finals at Melbourne Park on Friday.

Williams said: “It was a good match. I think Danielle is such an aggressive player. I’m glad I was able to get through that one in a tie-break.”

The 39-year-old had been due to play world number one Ashleigh Barty on Saturday but the Australian will now have a free passage through to the final.

Williams’ withdrawal is likely to be a precaution. In normal times, top players generally do not enter tournaments the week before grand slams and the world number 11 would likely not have wanted to play three consecutive days before the start of the Australian Open on Monday.

Barty, playing in her first tournament for nearly 12 months, had her own battle against American Shelby Rogers but came through 7-5 2-6 10-6.

The other semi-final will pit sixth seed Garbine Muguruza against former French Open finalist Marketa Vondrousova.

Muguruza won a confidence-boosting rematch of last year’s Australian Open final 6-2 6-2 against Sofia Kenin while Czech Vondrousova, who has struggled since losing to Barty in the Paris final in 2019, defeated Nadia Podoroska 4-6 6-3 10-4.