With her eye on the Olympics, Serena Williams is joining the United States for a Fed Cup playoff against Ukraine.

The best-of-five series on clay begins Saturday and Williams faces 17-year-old Elina Svitolina in the second singles match.

Williams, a 13-time Grand Slam champion, needs to play twice in the Fed Cup in 2012 to be considered by the U.S. Tennis Association for the Olympic team. She has won two Olympic doubles gold medals but none in singles.

"For me, any medal is great," Williams said. "If I win singles, it would be awesome. If I win doubles, it would be awesome. Or if I win mixed."

This is her second straight Fed Cup appearance after having played against Belarus in Worcester, Mass., in February.

This U.S. team, captained by Mary Joe Fernandez, also features Christina McHale, Sloane Stephens, and Liezel Huber.

The country that wins will be promoted to the main Fed Cup group in 2013 and be able to compete for the title. The loser will drop to World Group II.

In the top group this weekend, defending champion Czech Republic plays Italy in one semifinal, a meeting of the last two Fed Cup champions. Serbia is at Russia in the other semifinal. The winners will play for the title in November.

In Ostravia, Czech Republic, Lucie Safarova will be before a home crowd when she meets 2010 French Open champion Francesca Schiavone of Italy in a match between left-handers.

Petra Kvitova, ranked No. 3, will play the second singles for the host against Sara Errani, who won her third Barcelona Open title in four years on Sunday.

"It's more about the quality of the players," Schiavone said. "But, of course, the fast surface with the lefty service will be difficult. But we're ready."

In doubles, French Open champions Andrea Hlavackova and Lucie Hradecka will play the Italian pair of Errani and Roberta Vinci.

In Moscow, Anastasia Pavlyuchenkova of Russia takes on Jelena Jankovic of Serbia in opening singles. Two-time Grand Slam champion Svetlana Kuznetsova will face former French Open champion Ana Ivanovic in the second match.

Serbia has reached the semifinals of the tournament for the first time and features two former No. 1 players. Russia, a four-time champion, has beaten Serbia in all three of their previous matches, but is without its two top players: Maria Sharapova and Vera Zvonareva.

In doubles, Russians Maria Kirilenko and Elena Vesnina will face Bojana Janovski and Aleksandra Krunic.

"It's going to be a historic moment for us." Jankovic said. "Hopefully, we could make it into the final. It's been a long way to come up to this stage. It will be a tough match. We are playing against Russia and in Russia."