Roger Federer has spoken out following Martina Hingis' decision to hang up her racket after the WTA Finals event.
The 37-year-old Slovakian, who represents Switzerland in her professional career, will officially retire when the event finishes on Sunday.
Hingis has "retired" from the sport twice before, firstly in 2003 as a 22-year-old, and then in 2007.
Her most recent major success was winning the mixed-doubles US Open title at Flushing Meadows, alongside Jamie Murray.
They also won the mixed-doubles event at Wimbledon earlier in the summer.
Hingis retires as the World Number One doubles player, and a five-time Grand Slam champion.
In a statement, she said: "I think now it's definite. It's different, because before I walked away thinking I might come back.
"After a season like this, I think it's also perfect timing. You want to stop on top and not when you're already going backwards.
"I couldn't ask for a better finish."
And, following on from reaching the quarter-final of the Swiss Indoors Championship in Basel, the 36-year-old commanded the achievements of Hingis in her career.
"Martina was partially the one who showed me how it was all done," Federer said.
"I loved seeing her play in the last couple of months in doubles, her matches were just beautiful to watch.
"Martina has a huge passion for our sport. Future life remains tied to tennis, I’m almost impatient to know what she’s going to do now.
"Martina was partially the one who showed me how it was all done. It was great for Switzerland to have someone of her calibre. We were very lucky. I loved playing with her at the Hopman Cup, she was always super friendly, I love that about her.
"I’m not sad to see her retire, she’s been in the game for long enough, she seems at peace with her decision — that’s wonderful. I’ve always been a fan of her and I always will be."