Former US Open champion Juan Martin del Potro said his recovery from knee surgery had been challenging.
Next year's Australian Open is set to be delayed by a week or two.
Vladimir Putin paid tribute to the "mastery" of Daniil Medvedev after his victory at the ATP Finals.
Lewis Hamilton is set for a knighthood, reports have claimed, and Andy Murray says the F1 star's achievements make him an obvious candidate.
After becoming the ATP Finals champion, Daniil Medvedev said he wants plenty more battles with beaten opponent Dominic Thiem.
Dominic Thiem lost the showpiece match at the ATP Finals for the second year running as Daniil Medvedev emerged victorious.
Amid reports the Australian Open could start as late as April, organisers are still planning for the summer.
Daniil Medvedev beat Rafael Nadal for the first time in his career as he set up an ATP Finals showdown with US Open champion Dominic Thiem.
Novak Djokovic lost to Dominic Thiem for a second straight year in London, as the Austrian booked his place in the season-ending final.
Rafael Nadal looks set to have his work cut out against Daniil Medvedev after the Russian reached the last four without dropping a set.