World number two Jannik Sinner said Thursday he anticipates "a very, very difficult and tough challenge" as he prepares to defend his Shanghai Masters title, a day after winning the China Open.
The 24-year-old Italian dominated teenager Learner Tien to clinch his 21st ATP title in Beijing on Wednesday, before travelling down to Shanghai hours later.
With no Carlos Alcaraz, who has withdrawn because of "physical issues", Sinner's main rival in the ATP 1000 tournament looks to be four-time Shanghai champion Novak Djokovic.
"I have only one practice session to get ready, but let's see," Sinner said.
"It's going to be a very, very difficult and tough challenge, especially the first (match)... you never know what's going to happen."
Germany's 49th-ranked Daniel Altmaier is Sinner's first opponent.
Last year, Sinner beat Djokovic in the final, but the 38-year-old Serb is coming into the competition fresh after cutting back the number of tournaments he plays.
The number of matches in the men's and women's tennis calendar has been a major talking point in recent years.
World number one Alcaraz said Tuesday before pulling out of Shanghai that "they have to do something with the schedule", echoing the sentiments of fellow major champions Iga Swiatek and Coco Gauff.
Sinner said Thursday he didn't "want to criticise anything".
"Everyone thinks in different ways... I would say we can still choose as players," he added.