Roger Federer has opened up about his decision to skip the French Open and what it was like watching Rafael Nadal capitalise on his absence.
Federer recently returned to the ATP tour following a two-month break, skipping the entire clay-court season, including Roland Garros.
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Nadal made the most of the Swiss great's absence, making history as the first man to win the same grand slam 10 times.
Federer on Monday was asked what he made of his rivals' form while he was idle.
"What stands out is Rafa's 10th win at the French Open and Stan's great run in Paris as well," Federer told Tennis TV.
"The best players were in the finals and Rafa once again cemented himself as the greatest clay-court player of all time.
"He's also making a case to be one of the greatest of all time.
"I'm so impressed by how you can just dominate one tournament from start to finish throughout your entire career.
"It was very impressive, I was very happy for him."
Federer's return to action in Stuttgart last week proved brief as he suffered a shock defeat to fellow veteran Tommy Haas, but the Swiss remains at peace with his decision to take time away from the tour.
"Considering how well I felt going into Paris, it was surprisingly easy to take the decision and after making it I never had any regrets watching it or following the results," said the Swiss ahead of the Gerry Weber Open in Halle - an event he has won on eight occasions.
"I never thought, 'if only I was part of the tournament'. I was looking ahead to the grass season and enjoyed the time with my friends and family at home.
"For a long time the schedule was to play Paris but all of a sudden I just felt that I wouldn't be comfortable doing it. I didn't want to compromise the goal of the grass-court season, Wimbledon, the US Open and beyond.
"I felt that the French Open may potentially have a negative effect on what's to come. It may have been helpful, but I felt there was more risk that it would go the other way. Based on health, that’s why I decided to skip.
"But it's not a trend that I might follow in the future. I don't know what the future holds. This was just a one-off decision."
Reflecting on his three-set defeat to Haas earlier this week, Federer added: "It could have been better in Stuttgart, but then again I had match point. It wasn't like I lost 6-2, 6-2 and everything was terrible.
"A comeback is never simple, especially on grass where margins are so slim. It's a serve or a passing shot or a return that determines the outcome of the match.
"That's what it ended up being against Tommy, even though I felt I should have found a way home, having been a set and a break up."
Federer could not ask for a more comfortable setting for his next event, given his multiple successes in Halle.
"The history I have here, having come and played well so often, definitely should help me to play good tennis this week," he noted.
"I love playing here. I think I can come in here with good confidence."