Watch List: Sharapova, Halep lead Stuttgart field; Nadal in Barcelona

The Watch List highlights the must-know storylines for the upcoming week in tennis.

The Watch List highlights the must-know storylines for the upcoming week in tennis. This week, two of the WTA's top three women are in Stuttgart, Germany, for the Porsche Tennis Grand Prix, while Rafael Nadal and Kei Nishikori lead the field for the ATP in Barcelona and Gilles Simon and Gael Monfils highlight the field at the Bucharest Open.

Porsche Tennis Grand Prix

[Complete draw]

The No. 2 ranking is on the line this week in Stuttgart, with two of the most well-rested players, No. 2 Maria Sharapova and No. 3 Simona Halep, leading the field. Stuttgart is a notoriously tough field. The draw had No. 10 Carla Suarez Navarro and No. 11 Andrea Petkovic playing in the first round until Petkovic announced her withdrawal on Monday due to a left thigh injury sustained at Fed Cup. The fact that the tournament comes immediately after a tough Fed Cup weekend also makes it hard to predict. 

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However, Sharapova has owned Stuttgart the last three years. The three-time defending champion is 13-0 at the tournament. Stuttgart has served as a launching pad for her strong clay season runs as of late, which have seen her go on to win the French Open twice. Sharapova pulled out of Russia's Fed Cup tie in Sochi after a leg injury and an early exit in Miami. If she fails to make the semifinals this week she will lose her No. 2 ranking to Halep. If the two meet in the final, the winner will hold the No. 2 ranking. Why does the No. 2 ranking matter? It means not having to be in Serena Williams' half of the draw at any upcoming tournaments. 

Sharapova leads the top half of the draw and could face a very tough opening match against Charleston champion Angelique Kerber. Also in her half of the draw is a rested Petra Kvitova, who is playing her first tour event since shutting it down for two months due to exhaustion. Ana Ivanovic also looms if she can get her game together on her favorite surface. The bottom half of the draw is anchored by Halep and No. 4 seed Caroline Wozniacki. After opting to skip Fed Cup to focus on her clay preparations, Halep is in a good position to make the final. She could open against GarbineMuguruza. Also looming in her half of the draw are Suarez Navarro and an improved SabineLisicki.

Barcelona Open

[Complete draw]

Rafael Nadal and Kei Nishikori lead the field in Barcelona, where defending champion and top seed Nishikori looks to kick-start his clay season and Nadal goes for a confidence boosting title run. David Ferrer is also in the field, drawn into Nadal's half. 

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This is a big week for Nadal. His run to the semifinals in Monte Carlo, where he lost to Novak Djokovic in straight sets, was a positive one. He is not as far off his game as one might have thought after his play on the North American hard courts. In Barcelona he will be tested. He could open against Nicolas Almagro, who beat him here last year, then Fabio Fognini, who beat him on clay at the Rio Open in February, with Ferrer looming in the semifinals.  

In contrast, it's an easier path to the final for Nishikori, who opens against Teymuraz Gabashvili. The seeds in his half of the draw are Marin Cilic, Jo-Wilfried Tsonga, Tommy Robredo, Pablo Cuevas, Martin Klizan and Santiago Giraldo. With Cilic and Tsonga still working their way back into form, Nishikori should like his chances. 

One notable name in the draw that we haven't seen in a while: Nick Kyrgios. The Aussie teenager returns to the tour after a foot injury sidelined him after Indian Wells.

Bucharest Open

[Complete draw]

Gilles Simon and Gael Monfils are the top two seeds in Bucharest. Monfils had a fantastic week in Monte Carlo, where he beat Roger Federer and Grigor Dimitrov to make the semifinals. A title run in Bucharest would put him on the "dark horse" list for the French Open. He seems to have discovered the perfect balance between aggression and defense in his game.