World number one Jannik Sinner said he is not worried about a hip issue that had been troubling him over the last couple of months and that he is looking forward to getting back on court at the US Open tune-up tournament in Cincinnati this week.

The 22-year-old has struggled to shake off the injury he picked up in May in Madrid and looked to have aggravated it during a shock quarter-final defeat by Andrey Rublev in Montreal on Saturday.

However, Sinner put his struggles down to the intensity of recent matches after skipping the Paris Olympics due to tonsillitis.

"I feel quite good. Obviously I made nearly one week without practising before, and then after playing for two-three days in a row, a bit more than usual, (that) could (have had) a potential impact to the hip," Sinner told reporters.

"But I'm not afraid. I feel good with the hip, and I'm just looking forward to going back on court here." The Australian Open champion said conditions at the Cincinnati Open this week could prove to be a bigger test as he gears up for the US Open, which runs from Aug. 26-Sept. 8.

Jannik Sinner starts strong on busy day in Montreal

"Here usually I struggle a little bit to play because of the conditions but I'm looking forward to see my reaction this year, because it's a great test," said Sinner, who plays Tallon Griekspoor or Alex Michelsen in his opener.

"I believe this tournament can give you a lot of confidence for the US Open, which is the last Grand Slam we have. So in my mind, this is a very important tournament. "We go day by day ... I have a couple of days to prepare and hopefully show some good tennis."