The Biggest Storylines to Watch Ahead of the 2015 Rogers Cup

The 2015 Rogers Cup, with its dueling ATP and WTA tour tournaments, represents the first major test on the road to the U.S. Open. 

After Wimbledon, players scattered to areas around the globe to play in mid-level and smaller tournaments. Although No. 2 Roger Federer and No. 7 David Ferrer withdrew from the tournament, most of the world's top players will return to compete in perhaps the biggest stop on the U.S. Open series.

The ATP's tournament begins Friday in Montreal, and the WTA's will get under way Saturday in Toronto. 

Serena Williams and Novak Djokovic are top seeds. With Williams and Djokovic holding massive points leads, the No. 1 rankings are non-issues.

The biggest storylines revolve around injuries, slumps, comebacks and up-and-coming players. The following are what people will be talking about as the ATP and WTA make their way to the Great White North.

Dominic Thiem Time

ALAIN GROSCLAUDE/Getty Images

Dominic Thiem kisses trophy after winning The Swiss Open in Gstaad.

Dominic Thiem has won two titles in two weeks, and now that he's reached the semifinals in Austria, he could win his third title in three weeks. The 21-year-old is on a hot streak. He won nine straight matches before falling in the semifinals in Austria.

His tournament titles have come at lower-level events, but Thiem has been on a roll. Thiem could be ranked as high as 17th come Monday. Keep an eye on this up-and-coming player. 

Eugenie Bouchard's Homecoming Redo

Streeter Lecka/Getty Images

Eugenie Bouchard hits a forehand during the 2014 Rogers Cup in Montreal.

Last year, Eugenie Bouchard arrived at the Rogers Cup tournament as a budding superstar ranked No. 8. She had just reached the Wimbledon final. Even after a crushing loss to Petra Kvitova, Bouchard's return to her native Montreal was supposed to be a homecoming celebration.

Instead, she lost her first match to Shelby Rogers. The Rogers Cup would become the beginning of a massive slump for the Canadian.

Now, ranked No. 25, Bouchard hopes some home cooking can help nurse her career back to health. 

Besides dropping out of the top 20, Bouchard split with coach Sam Sumyk.

Bouchard, the so-called most marketable athlete, seems to be suffering from a tennis identity crisis. 

Note to Princess Eugenie: Whether you seek to be the queen of endorsements, like Maria Sharapova, or the queen of tennis, like Serena Williams, you have to get your game back on track. 

Serena Williams' Right Elbow

Streeter Lecka/Getty Images

Serena Williams hits a forehand during 2014 Rogers Cup semifinal.

Serena Williams arrived in Toronto having played just one match since her Wimbledon triumph. She withdrew from the Swedish Open and Bank of the West tournaments with a right elbow injury.

With plenty of room to spare in her points lead over No. 2 Sharapova, Williams has little to prove at the Rogers Cup. The one incentive might be winning the U.S. Open series points race for bonus money.

In the past two years, she's won the U.S. Open series twice to capture an additional $1 million to go with her prize money. Last year, she won the U.S. Open and the series to bring in a record $4 million in prize money. 

Has the time off just been precautionary? Or is there a more serious issue with her elbow? All eyes will be on Williams to see if that elbow might stand in the way of her winning a calendar-year Grand Slam. 

Andy Murray's Washington Washout

Nick Wass/Associated Press

Andy Murray walks off the court after losing his match at the 2015 Citi Open.

Andy Murray took a tour of the White House just before his first match at the Citi Open, and that was the highlight of his stay in D.C. Murray lost his opening match to unseeded Teymuraz Gabashvili.  

What a disappointing outing for the No. 3 player. Murray, the top seed at the Citi Open, missed out on a chance to take 500 points in a tournament without three of the Big Four or Stan Wawrinka. What a missed opportunity to gain ground on Federer.

Rafa's Reboot

Ian Walton/Getty Images

Rafael Nadal hits a backhand at the 2015 Wimbledon championships.

Rafael Nadal's win at Hamburg ended the Spaniard's mini-slump this season. But that was on clay. This is hard-court season, where Nadal still needs to find his footing.

If the season ended today, Nadal would be sixth in the Race to London. 

Despite Nadal's off year, he's in the perfect position to finish strong. Last season, Nadal skipped the U.S. Open series due to a wrist injury. So every match he plays this summer is ranking points gold. 

Although the hard surfaces are not his favorites, the U.S. Open tune-ups could be just what Rafa needs to fight his way back to the top.