Roger Federer returned a compliment to Andy Murray and looked ahead to a potential grass-court meeting the morning after a gruelling third-round win at Roland Garros.
Federer made round four at the French Open but was so drained by the experience that he suggested he could yet withdraw from the tournament as he looks to build up fitness ahead of Wimbledon.
The Swiss superstar entered the clay-court major with a 1-2 record for the year, most recently losing to Pablo Andujar in Geneva last month.
However, Federer has strung together three straight wins in Paris, beating Dominik Koepfer in the last 32 in a match that finished in the early hours of Sunday in the French capital.
The match started at 21:00 local time (20:00 GMT), in line with a coronavirus-enforced curfew that ensured the stands were empty on Court Philippe-Chatrier.
Despite the strange experience and a determined opponent, Federer came through in four sets after three tie-breaks to continue his pursuit of a record-breaking 21st grand slam title.
During the match, which finished at close to 01:00 local time (00:00 GMT), fellow great Murray posted on Twitter: "I'm not bothered by the outcome of this match at all.
"Just seeing Federer at 39 off the back of two knee surgeries playing to an empty stadium at 12:30am getting fired up is inspirational to me. Do what you [love]."
Murray himself has overcome a series of major injuries to remain on the ATP Tour, even backtracking on a retirement pledge in 2019.
So, Federer replied on Sunday: "Thank you Sir Andy, the feeling is mutual. You gotta love it. See you on the [grass]."
Thank you Sir Andy, the feeling is mutual. You gotta love it See you on the https://t.co/6Jln8V6vSw— Roger Federer (@rogerfederer) June 6, 2021
There was no further comment on potentially quitting the French Open, where Federer is appearing for only the second time since the start of 2016 – he made the semi-finals two years ago.
His sublime major form has slowed over the past decade, making only nine finals compared to 22 in the previous 10 years.
If Federer is able to continue, he faces a tough ask on Monday, taking on Matteo Berrettini, who has become the first Italian to reach the last 16 of all four slams in the Open Era.