Roger Federer during loss to Rafael Nadal at ATP Championships in London.
Each year the ATP and WTA tours produce surprising developments, spectacular matches and a few oddities. In 2013, Marion Bartoli's fairytale win at Wimbledon was among one of the more fascinating stories. Bartoli then shocked the tennis world by announcing her retirement just weeks later.
Watching Federer falter became a recurring theme at Grand Slams. Whether Federer switched rackets, fired a coach or tweaked his schedule, his struggles made the news. As we enter 2014, expect more of the same.
Another note-worthy storyline will be who among the up and coming young players will have a breakthrough year. Will it be Sloane Stephens, Simona Halep or Eugeine Bouchard on the women's side? What about Milos Raonic, Jerzy Janowicz or Kei Nishikori on the ATP tour?
There are plenty of heart-warming, compelling stories among the hundreds of players and venues on both tours.
But this list is about what will be the hottest stories in 2014. The list includes Twitter-worthy topics that will yield hashtags and dominate comments sections. These are the tennis storylines that will matter most in 2014.
Victoria Azarenka at the U.S. Open
Is Vika for real? That's the question that will follow Victoria Azarenka until she offers an answer to her underwhelming finish in 2013.
She entered 2013 ranked No. 1 and was considered the singular threat to Serena Williams. She enters 2014 ranked No. 2, but more than 5,000 points behind Williams. With a surging Li Na on her tails, Azarenka's validity and relevance on tour will be tested.
John Isner and Andy Roddick play in a charity exhibition in Florida.
The lack of top-notch American male players on tour is an old story. But that doesn't mean it won't continue to be a big story. It might even get bigger if the dearth of talent behind John Isner gets worse.
With James Blake and Andy Roddick retired, the glory days of the great American male tennis player are gone too.
Those who once looked hopeful, such as Ryan Harrison and Donald Young, appear more like flameouts.
Make no mistake, the lack of a serious American male contender impacts television ratings and ticket sales in the U.S. For those reasons this will continue to be a big story.
Maria Sharapova takes a spill at 2013 Wimbleon.
But it's unclear what type of shape Sharapova's in. She hasn't played a match since this summer in Cincinnati. She's slated to play in Brisbane later this month.
The marketing machine behind brand Sharapova will keep her in the news. How she plays upon her return will determine if it's all good news.
Jerzy Janowicz goes for a forehand.
Every year there are stories about who will emerge as the next big thing.
Although veterans like Nadal and Williams stay on top, the next big thing is always a huge story.
Fans in London express their feelings about an absent Andy Murray.
Andy Murray's return from back surgery will matter most to those who seek a break from the monotonous Djokovic-Nadal matchups.
Murray is a two-time Grand Slam winner, which puts him in the elite category on the ATP tour. With Federer fading, Murray is also among the few marquee names left on tour.
How he performs post surgery will be a big story in 2014.
Viktor Troicki, seen here at Wimbledon 2013, was one of the biggest names flagged for doping violations.
How the International Tennis Federation handles its anti-doping program will be the main story in 2014. Players such as Federer have called for an aggressive approach, including biological passport testing.
Other players have been critical of how the ITF schedules testing. Djokovic and Nadal questioned alleged advice given to Troicki by an ITF official.
Roger Federer waves to the crowd as he leaves the court at the 2013 U.S. Open.
As long as Federer is on tour, anything he does will be newsworthy. Considered one of the greatest players of all time, Federer has cemented his place among the game's legends no matter what happens for the rest of his career.
But how the rest of his career unfolds will continue to make headlines. If he spends another year mired in a slump, that's a big story. Another Slam is an even bigger story.
No longer invincible, Federer remains relevant because he is a fans' favorite.
Is it Djokovic the conqueror? Maybe he's Djokovic the choke-a-vic? Even after winning six Slams, Djokovic finds himself in pursuit of respect.
As great a player as he is, Djokovic has the misfortune of having a career flanked by greats like Federer and Nadal. How will Djokovic handle the fall of Federer and the resurgence of Nadal? Perhaps the greatest player to play third wheel, Djokovic will stay in the headlines in 2014.
Rafael Nadal during the ATP Championships in London.
Rafa is back. The resurgent Nadal was one of the biggest stories in 2013. Can he continue this incredible run? Will he win a ninth French Open? Could he match Federer in Slam totals?
Whatever he does, Nadal will be big news. He's not only one of the game's biggest stars, the way in which he returned to reclaim the No. 1 ranking makes him one of the most fascinating people in sports.
Serena Williams with the 2013 U.S. Open trophy
Serena Williams is in a league of her own on the tour. Unlike on the ATP tour where there are three guys with double digit Slam totals, Williams is the only current WTA player to accomplish that.
Williams needs just one Grand Slam to tie legends Martina Navratilova and Chris Evert.
Her 5,200 point lead in the rankings ensures that she will remain No. 1 for a while. Her 78-4 record last year shows how dominant she can be when she is healthy. All eyes will be on the No. 1 player as she chases Grand Slams.