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Roger Federer (left) and Andy Murray (right) have battled injuries and fatigue. Getty

The unexpected comebacks of Roger Federer and Rafael Nadal, as well as injuries to some marquee stars, have dominated the headlines of the 2017 ATP season. The storylines take on added importance entering the final Grand Slam of the year, the U.S. Open, which begins on Aug. 28.

Notable absentees from the U.S. Open include Novak Djokovic and Stan Wawrinka, both of whom are done for the year after failing to capture a Grand Slam title. Kei Nishikori, a U.S. Open finalist in 2014, announced on Wednesday that a right wrist injury will force him to miss the rest of season.

It has been a particularly disappointing year for Djokovic. One of the all-time great Australian Open competitors was bounced in the second round in Melbourne and when it came to defending his French Open title, Djokovic was eliminated in the quarterfinals. Withdrawing from the Wimbledon quarterfinals completed a frustrating year for Djokovic, who ultimately decided to shut down his season to rest his ailing right elbow.

"After a year and half of carrying an elbow injury that has culminated in the last couple of months, I made the decision not to play anymore for the rest of the 2017 season," Djokovic said in a Facebook Live video posting on July 26.

Wawrinka, the defending U.S. Open champion, had to cut his season short because of a lingering knee problem. Despite crashing out of Wimbledon in the first round and winning just one tournament, the 32-year-old had enjoyed several impressive runs this year. Wawrinka went five sets with Federer in the semifinals of the Australian Open and lost to a particularly dominant Nadal in the French Open final before admitting on Aug. 4 that his knee needed treatment.

Wawrinka seemed to know that rest was necessary immediately after an early exit in London. When asked what was next after his Wimbledon defeat, the 32-year-old had said, "What's sure is that I'm going to take the time I need to feel ready again physically."

There have also been nagging injuries for Andy Murray and Federer. Murray has been dealing with hip problems, while Federer has dealt with a nagging back.

So with plenty of star power out or hobbled, who has the best shot at capturing the single's title at Flushing Meadows?

Roger Federer

How serious is Federer's back problem? The answer will likely become clear after the first round. The 35-year-old has looked sharp all year and it's quite possible that skipping the Cincinnati Masters will provide a boost to his conditioning at Flushing Meadows. Another deep run can be expected if Federer gets a comfortable draw and shows the same type of consistency he has displayed throughout the season. He has gotten the best of Nadal on hard court this year and owns a stellar 35-3 overall record in 2017.

Betting Odds: +125

Rafael Nadal

The slim field may open the door for Nadal. The clay-court specialist defied expectations in the other hard-court Grand Slam — Nadal reached the final of the Australian Open in January — and is the only top player who seems to be playing at full strength. Nadal, who has a 48-8 record in 2017, bowed out early in the Rogers Cup in Montreal but was sharp at three hard-court tournaments in the late winter, reaching the final of the Mexican Open, and losing to Federer at Indian Wells and the Miami Open. Nadal has won the U.S. Open twice and this might be his best chance to win it again.

Betting Odds: +250

Andy Murray

The Scot has been hobbled by a hip problem and hasn't played since losing to Sam Querrey in the Wimbledon quarterfinals. It's anyone's guess if Murray will be at full strength to compete in New York, but he has a mostly performed well in the tournament, reaching at least the quarterfinals in five of the last six years. An inspired Murray can still go deep at the U.S. Open, though Murray's mother told Reuters on Tuesday that "the last two years have taken a lot out of him."

Betting Odds: +700

Others

Alexander Zverev (+700) is one of the best young players in tennis despite a poor record in Grand Slam tournaments. The 20-year-old native of Hamburg, Germany, defeated Federer 6-3 6-4 at the Rogers Cup, immediately boosting his profile. Zverev is a talent, as evident by a second serve that can top 130 miles per hour.

Marin Cilic (+1,800) is a legitimate dark horse to win in New York after taking the title in 2014 in his lone Grand Slam. The Croatian is coming off a trip to the Wimbledon final and an impressive quarterfinal appearance at the French. However, he was eliminated in the second round of the Australian Open.

This could be a semifinal packed with underdogs, though they are not getting much love from oddsmakers. Milos Raonic (+2,000), Dominic Thiem (+2,500) and Nick Kyrgios (+2,800) are among the top contenders.