Indeed the way last year concluded, the new season shouldn't lack in drama.
Here's why ...
He was, don't forget, ranked third in July just before deciding to skip the rest of 2016 to rehabilitate his knee.
Federer was due to make a high-profile comeback earlier this month in the exhibition IPTL but didn't play due to, as the struggling Asian-based league put it, the "current economic climate in India and uncertainty of spending money."
He'll take to the court in the first week of January at the Hopman Cup, a team event in Perth.
Later, if Federer does end his four-year title drought at majors, he would become the second oldest man to win a grand slam in the Open Era, behind Ken Rosewall.
Wimbledon remains the most likely venue, given it has been Federer's most successful major with seven titles.
Sharapova is scheduled to return at the end of April, at which time the five-time grand slam winner -- and for most of the last decade the richest female athlete in the world -- would have served her 15-month suspension for testing positive for meldonium.
The head of the WTA, Steve Simon, says he will welcome her back
, but how will the fans and her fellow players respond?
The locker room may be icier.
WTA Finals winner Dominika Cibulkova, shortly after Sharapova admitted to the failed drug test, labeled her "unlikeable, arrogant, conceited and cold."
Doubles grand slam winner Kristina Mladenovic claimed that Sharapova "wasn't really nice nor polite." Sharapova's Fed Cup teammates Elena Vesnina and Svetlana Kuznetsova have defended her, though.
Could Sharapova win a grand slam? Don't count her out, especially if Williams isn't in her way. Sharapova's motivation is bound to be soaring.
What will Kyrgios do next?
It's extremely rare for the ATP to sanction one of its own players but the men's tour has done it two seasons in a row to Nick Kyrgios. Hence the "bad boy" tag.
After Kyrgios directed a lewd on-court sledge at Stan Wawrinka and his girlfriend in 2015, the ATP fined him $10,000 and handed him a suspended ban; then this October he was suspended for eight weeks
-- through the middle of January -- and fined more than $40,000 for not trying in a match at the Shanghai Masters.
Kyrgios, like Federer, will make his return at the Hopman Cup, which isn't an ATP event and thus not related to the suspension.
Currently without a coach, the likes of eight-time grand slam champion Jimmy Connors and Kyrgios' fellow Aussie, former Wimbledon finalist Mark Philippoussis, have offered to work with the 21-year-old, but just how much motivation Kyrgios has to make changes remains to be seen.
He told the New York Times in August that he planned to retire by 27 and has often claimed he likes basketball much more than tennis.
Serena's quest for No. 23
Williams' charismatic coach, Patrick Mouratoglou, set the bar high for his charge when discussing future grand slam titles. He is targeting 30
, eight more than her current haul.
Given her age -- 35 like Federer -- that may be optimistic, but odds are that the American will edge ahead of Graf, who also holds 22 majors to share the Open Era record: Williams has won a major in each of the past five seasons.
Also like Federer, she has been slowed by injuries. Though Williams -- especially in recent times -- has never been one to overload her schedule, she was limited to eight tournaments in 2016 and, hindered by shoulder troubles, shut down her season post the US Open for the second year running.
Williams didn't compete in the IPTL as originally planned because of the aforementioned financial constraints of the league; she will return the first week of January and make her first appearance at Auckland's ASB Classic.
If you listen to Djokovic's now former coach, Boris Becker
, the Serb didn't practice hard enough in the second half of 2016.
"He has not spent as much time on the practice court as he should have in the last six months and he knows that," Becker told Sky in early December after he cut ties with Djokovic.
Becker had earlier told CNN -- while he was still working with the player -- that Djokovic suffered from the absences of both Federer and Rafael Nadal.
The Spaniard, like Federer, will be returning to the tour after a break to recover from injuries, and the 14-time grand slam winner has added his friend and former world No. 1 Carlos Moya to his coaching staff.
With both resurfacing in 2017 and Djokovic losing his No. 1 ranking to Andy Murray in November, he shouldn't have any issues with motivation.
There were, too, injuries and much speculated personal issues that took a toll on the 12-time grand slam champion.
It culminated in an alarming performance against Murray in the final of the World Tour Finals, when Djokovic had a chance to regain the No. 1 ranking.
The Australian Open has been Djokovic's stronghold, having won the tournament five of the past six seasons, so if Djokovic fails to repeat as champion his slump will escalate further.