Likely just a new coach, but no one seems to know exactly.
There is always that slim chance of retirement, but that seems unlikely. Maybe he will miss more time from his injury?
A Baker's Dozen Predictions for the New Year, all of them guaranteed to come true:
Four different players will win Grand Slams, none of whom will be Roger Federer
Novak Djokovic will end the year #1 once again
Grigor Dimitrov will remain in the Top Five and may even challenge for #1
Thiem, Zverev and Goffin will all continue to prosper and remain in the Top Ten
Elina Svitolina will end the year #1
Sloane Stephens and Madison Keys will crack the Top Ten
Nick Kyrgios will finally land in the Top Ten
Denis Shapovalov's rise will slow, though by end of the year he should be in the top 25
Jack Sock will win a Grand Slam (after which hell will indeed freeze over)
Milos Raonic will not return to the Top Ten
Hyeon Chung will finish in the Top Twenty (I love his footwork. Seriously)
Andrey Rublev will finish slightly ahead of Chung.
Roger Federer will start musing about retirement.
Serena Williams will play some tournaments, but not enough to get her back to #1.
“Having played practice sets here in Brisbane with some top players, unfortunately this hasn’t worked yet to get me to the level I would like, so I have to reassess my options. Obviously continuing rehab is one option and giving my hip more time to recover. Surgery is also an option but the chances of a successful outcome are not as high as I would like, which has made this my secondary option, and my hope has been to avoid that. However, this is something I may have to consider, but let’s hope not.”
Anyway, I somewhat expected her to skip the Aussie Open. Too short of a turnaround to get her fitness back up to speed coming off of a caesarean delivery.