"Many people see how beautifully Roger Federer plays, but they underestimate how good an athlete he is" - Dominic Thiem

Roger Federer was forced to withdraw from the US Open and end his 2021 season due to a knee injury, for which he will be getting a third surgery in 18 months. The Swiss' absence at Flushing Meadows is in addition to that of 2019 and 2020 champions Rafael Nadal and Dominic Thiem, who have withdrawn from the event due to foot and wrist injuries respectively.

But Thiem is still making is presence felt at the tournament, in the form of a guest analyst for Tennis Channel. While commenting on a video of an old Roger Federer training session, the 27-year-old showered rich praise on the 20-time Grand Slam champion's movement and hand-eye coordination.

"Very, very difficult exercises, but Roger makes it look easy, like everything he does. It's a great video but super difficult," Thiem said.

"I think many people underestimate how good an athlete he is," the 27-year-old added. "I mean, you can see it in this video. How he moves and all this hand-eye coordination, it's simply amazing."

"Roger makes it look easy...like everything he does."-@ThiemDomi Before Roger Federer was winning Majors, he was playing tennis while dribbling a basketball. Naturally.@RogerFederer | #TCLive | #USOpen pic.twitter.com/3rvOQGggCj

— Tennis Channel (@TennisChannel) August 30, 2021

Dominic Thiem and Roger Federer have faced each other seven times on tour, with Thiem leading the head-to-head 5-2. Although the two have never met at a Major, the Austrian has defeated Federer in some big matches - including the 2019 Indian Wells Masters final and the grasscourt semifinal at Stuttgart in 2016.

Dominic Thiem further went on to claim during his Tennis Channel appearance that although fans focus on how "beautifully" Roger Federer plays the game, they tend to underestimate how good of an athlete he is.

"Many people just see how beautifully he plays. I mean, I can totally understand it," Thiem said. "But I think many underestimate what a good athlete he is and that's so much hard work. And you see how he does it in that video already, it's stunning."

Roger Federer and Dominic Thiem both set for a 2022 return

Dominic Thiem

Roger Federer only played four tournaments in all of 2021, after skipping a majority of the 2020 season to deal with knee injuries. The Swiss has won seven matches at Grand Slam level this year, reaching the fourth round at Roland Garros and the quarterfinals at Wimbledon.

However, problems in his knee have raised serious concerns over whether he will be able to be competitive when he returns. The 40-year-old last won a tour-level title in 2019, and his last Major triumph came at the 2018 Australian Open.

Dominic Thiem, meanwhile, still has his wrist in a splint after the injury he picked up at Mallorca in June. The Austrian is hoping that the injury heals by the end of October, after which he can start training again.

Thiem is targeting a return to action at next year's Australian Open, but it is likely he will be outside the top 10 of the rankings by then.