Roger Federer is to undergo further knee surgery to give himself a "glimmer of hope" of returning to tennis.
The procedure is set to keep the 40-year-old out for "many months".
Here, we take a look back at Federer's remarkable career in numbers.
20 – grand slam titles, the most won by any man – a record shared with Rafael Nadal and Novak Djokovic.
31 – grand slam finals.
23 – consecutive appearances in grand slam semi-finals, an all-time record.
36 – consecutive appearances in grand slam quarter-finals.
65 – consecutive grand slam appearances from the Australian Open in 2000 to the French Open in 2016.
8 – Wimbledon titles, the most of any man.
6 – Australian Open titles.
5 – US Open titles.
1 – French Open title.
1,251 – career matches won out of 1,526.
369 – match wins in grand slams.
310 – weeks spent at world number one, 237 of them consecutively.
36 – at 36 years and 320 days, Federer was the oldest world number one in ATP history.
5 – Federer has reached the final at every grand slam at least five times.
103 – career titles, second in the Open era behind Jimmy Connors.
6 – titles won at the ATP Finals, an all-time record.
10 – titles won at the ATP events in Basel and Halle.
12 – titles won in 2006, his most successful season.
92 – matches won from 97 played in 2006.
65 – consecutive matches won on grass from 2003 to 2008.
4 – Federer reached the finals of all the grand slams in three different seasons.
2 – Olympic medals; gold in doubles with Stan Wawrinka in 2008, silver in singles in 2012.
24 – losses to his great rival Rafael Nadal from 40 matches.
130,594,339 – career prize money (US dollars).
