Ryan Harrison (above) has replaced Mardy Fish on the U.S. Davis Cup team. (Mike Ehrmann/Getty Images)
The Watch List spotlights the must-know storylines for the upcoming week in tennis. This week, the Davis Cup quarterfinals are contested and the Williams sisters compete in Charleston, S.C.
• Davis Cup: The Freedom Fries Special in Monte Carlo headlines the World Group quarterfinals, while Serbia and Spain will be competing without Novak Djokovic and Rafael Nadal, respectively. Here's a look at the matchups:
-- United States at France: The tie was turned upside down Monday when the USTA confirmed that No. 9 Mardy Fish pulled out with what's being described as a "minor health scare" related to "extreme fatigue." Ryan Harrison will replace Fish, who won two matches in the Americans' 5-0 sweep of Switzerland in February. Harrison got his first career Davis Cup victory in that first-round upset, winning a dead rubber against Michael Lammer.
Not to be outdone, the French tennis federation announced that 14th-ranked Gael Monfils, who just returned from a month-and-a-half absence to heal his knees, is also out, this time with an abdominal injury. No replacement has been named, though Gilles Simon and Richard Gasquet would be the two obvious choices.
How much the change will affect the Americans is tough to say. Fish has been struggling, failing to win back-to-back matches this year until stringing together three in a row at the Sony Ericsson Open. This could be a great opportunity for the hyper-competitive Harrison, who has never faced French No. 1 Jo-Wilfried Tsonga or Gasquet and lost a three-setter to Simon at Indian Wells . As for John Isner, can he shoulder the load of being the top American for the weekend and back up his memorable clay win over Roger Federer? If Big John can grab two points for the Americans, it would be officially time to stop wondering if he can do well on clay and start expecting it.
-- Serbia at Czech Republic: Serbia is without Djokovic for the second tie in a row, meaning No. 8 Janko Tipsarevic and No. 27 Viktor Troicki will lead the team into Prague. Based on singles rankings, this matchup looks like a toss-up. No. 7 Tomas Berdych and No. 24 Radek Stepanek will anchor a Czech team that narrowly lost to Djokovic-led Serbia in the 2010 semifinals. After a strong start to 2012, Berdych has hit a bit of a speed bump, with losses to Nicolas Almagro in Indian Wells and Grigor Dimitrov in Miami. If this tie turns on doubles, the edge is with the Czechs. They have won six straight doubles rubbers while the Serbs have dropped five of their last eight.
-- Croatia at Argentina: The 2011 runner-up plays host to a tricky Croatian team in Buenos Aires. Any match involving Ivo Karlovic can get complicated quickly, but there's too much clay talent on the Argentine team. Juan Martin del Potro, David Nalbandian and Miami semifinalist Juan Monaco give captain Martin Jaite quite a few options against Karlovic and Marin Cilic.
-- Austria at Spain: No Rafa? No problem. David Ferrer, who said last year that he didn't plan to play Davis Cup in 2012, is back in the fold, along with Almagro. That alone should be enough for the Spaniards, as Austria's Jurgen Melzer has had three early exits since winning Memphis on a broken toe in late February. Go ahead and pencil in defending champion Spain for the semifinals.
• Charleston: The Family Circle Cup field took a hit Sunday when Agnieszka Radwanska withdrew because of a "back injury." Boy, that Sony Ericsson Open trophy must be heavy if players are throwing out their backs hoisting it. But in all seriousness, it would have been fun to see Radwanska take to the green clay against the likes of Serena and Venus Williams and Samantha Stosur. As it stands, the Charleston field is still buzz-worthy. With Radwanska out, Stosur becomes the top seed (best not to tell her that), followed by Marion Bartoli, who snapped Victoria Azarenka's 26-match winning streak last week.
But all eyes will be on the Williamses. Venus, who is chasing Olympics qualification, climbed back inside the top 100, at No. 87, after her quarterfinal appearance in Miami. A spot in the top 56 in the June 11 rankings would position Venus for direct acceptance into the London Games. As for Serena, if Miami showed us anything, it's that she needs match play after a long post-Australian Open layoff. Her footwork was borderline clumsy at times, but you get the sense that if she commits to the clay season and stays injury-free, she could do something special in Paris. That quest starts in Charleston.The Original 9 reunite will host