Garbine Muguruza is expecting rival Serena Williams to return to tennis "as dangerous as she has always been" next year.

The 23-year-old Spaniard has taken full advantage of Williams' time out of the sport because of pregnancy to take over as world number one after reaching the US Open last-16 earlier this month, but was mainly due to her first Grand Slam win at Wimbledon.

Williams gave birth to a baby girl this month and will now be looking to return to action in 2018 and Muguruza knows she will provide a stern challenge to her number one status when back on the court.

On the 35-year-old, 23-time Grand Slam winner, Muguruza told EFE: "I think she will return to competition and she will be as dangerous as she has always been.

"It is incredible that after being a mother and the best [player in the world], she still has the will and the hunger to return to competition."

On her bid to remain at the top of the world rankings, Muguruza, who beat Caroline Garcia 6-2 6-4 on Friday to reach the Tokyo Pan Pacific Open semi-finals, added: "I slept peacefully when I achieved it, but at the same time I am aware of the burden I am shouldering.

"On one hand, what an achievement. But there is still a lot of work to do and it will be difficult."