Watch List: Roger Federer, Serena Williams back in action on clay

Roger Federer is set to play clay-court events the next two weeks. (Clive Brunskill/Getty Images) The Watch List spotlights the must-know storylines for the

Roger Federer is set to play clay-court events the next two weeks. (Clive Brunskill/Getty Images)

The Watch List spotlights the must-know storylines for the upcoming week in tennis. This week, while many of the top players are resting, Roger Federer and Serena Williams are playing clay-court tournaments in Europe.

bet-at-home Open

[Complete singles draw]

For a sport that struggles with the black cloud of gambling, the cringe-worthy-named bet-at-home Open in Hamburg, Germany, isn't exactly the most endearing stop on the ATP Tour. But Federer's unexpected appearance has given the ATP 500 event a dominant on-court storyline.

After a stunning second-round loss at Wimbledon, Federer committed to small clay-court events in Hamburg this week and Gstaad, Switzerland, next week. Getting back on court quickly makes sense, given his limited playing schedule this year, as does the need to chase points and confidence before the last Grand Slam tournament of the year, the U.S. Open. But why would Federer want to go back to clay for two weeks when all the relevant tournaments from here on out are on hard courts? One theory making the rounds is that Federer has finally decided to experiment with a racket change. These two events could be his attempt to test it in competition.

Federer, ranked No. 5 for the first time in a decade, tops the Hamburg field along with Tommy Haas, Nicolas Almagro and Wimbledon semifinalist Jerzy Janowicz, who is up to a career-high No. 17. Federer could face Ernests Gulbis in the third round and Janowicz in the semifinals. Also in the field is a red-hot Fernando Verdasco, who is 10-3 since switching from a Dunlop to Babolat racket in Eastbourne, England. Gael Monfils is also in the draw, which means Federer won't be a lock for Hot Shot honors this week.

Collector Swedish Open

[Complete singles draw]

I'm going to ask the question on everyone's mind this week: Why in the world is the top-ranked Williams playing an International-level clay-court tournament in Bastad, Sweden, just one week after Wimbledon? Now I'm going to ask the second question on everyone's mind: How many krona had to be put up to guarantee her appearance? Aside from the hefty appearance fee, this stop has been a head-shaker ever since she confirmed her entry last fall.

She arrived on Saturday with Patrick Mouratoglou to quite a bit of fanfare:

http://www.youtube.com/watch?v=-hJkf1nMnhE

Williams, seeking her first International-level title, leads the 32-player draw. No. 23 Simona Halep, who has been on an incredible tear, is the second seed. She has won her last three non-Slam tournaments since losing to Williams in the semifinals of the Italian Open in mid-May. After Halep, the quality of the field drops precipitously. No. 57 Tsvetana Pironkova is the No. 4 seed. That says it all.

That isn't to say the tournament won't yield some interesting matches. Most intriguing is a potential second-round match between Williams and junior No. 1 Belinda Bencic, who received a wild card. The 16-year-old, who won the girls' titles at Roland Garros and Wimbledon, is coached by Martina Hingis' mother, Melanie Molitor. She's the real deal. It will be fun to see how she fares against the WTA No. 1. Aside from that, a final between Williams, who is 23-0 on clay this year, and the streaking Halep could be great.

Nurnberger Gastein Ladies

[Complete singles draw]

Andrea Petkovic is one name to watch in this International-level clay-court tournament in Bad Gastein, Austria. Petkovic showed some good form at the end of the pre-Wimbledon clay season, winning the $100,000 ITF event in Marseille, France, and making the final in Nurnberg, Germany, the following week. She beat the likes of Jelena Jankovic, Anabel Medina Garrigues and Monica Puig (by a 6-0, 6-0 scoreline) in that stretch. At Wimbledon, Petkovic lost to Sloane Stephens 8-6 in the third set in the second round. Given the field (No. 31 Mona Barthel is the top seed), a title here isn't out of the question for the former world No. 9, who is ranked No. 61. It would be her first since 2011.

Claro Open Colombia

[Complete singles draw]