WIMBLEDON, England — Defending champion Rafael Nadal will face a tough draw at Wimbledon if his aching knees allow him to play, with a likely second-round matchup against former No. 1 Lleyton Hewitt and Andy Murray possibly waiting in the semifinals.

Five-time champion Roger Federer was placed in the same half of the draw as Novak Djokovic on Friday, and could face the Serb in the semifinals as he bids for a record 15th career Grand Slam title.

The Williams sisters were placed in opposite sides of the draw, setting up a potential final matchup. Defending champion Venus Williams is aiming for her sixth singles title on Centre Court, but may first have to overcome top-ranked Dinara Safina in the semifinals. Serena could play fourth-ranked Elena Dementieva for a spot in the final.

Murray is coming off his first grass-court title at the Queen's Club and could provide a major obstacle for Nadal, whose participation is in doubt because of his knee problems. Nadal is expected to announce later Friday whether he will defend his title.

Nadal lost an exhibition match to Hewitt on grass on Thursday and will play Stanislas Wawrinka in another two-set match before making his decision. He pulled out of the Queen's tournament to rest his knees after a fourth-round loss to Robin Soderling at the French Open, his first defeat at Roland Garros.

Nadal was drawn against Arnaud Clement of France in the first round, and Federer will play Yen-Hsun Lu of Taiwan. Murray takes on Robert Kendrick of the United States, and Djokovic plays Julien Benneteau of France.

Safina was drawn against Lourdes Dominguez Lino of Spain in the first round. Venus Williams will take on Stefanie Voegele of Switzerland and Serena plays Neuza Silva of Portugal.

Andy Roddick was placed in Nadal's half of the draw and could face the defending champion in the quarterfinals, if the American gets past Jeremy Chardy of France in the first round and potentially Nikolay Davydenko in the fourth.

Federer faces a seemingly easier path than Nadal, but could face Soderling in the fourth round and either seventh-seeded Fernando Verdasco of Spain or No. 9 Jo-Wilfried Tsonga of France in the quarterfinals.

Former women's champion Maria Sharapova, who is still trying to return to form after a lengthy injury layoff, starts against Viktoriya Kutuzova of Ukraine and could face Serena Williams if she makes it to the quarterfinals.

Safina, who is still looking for her first Grand Slam title, may face Svetlana Kuznetsova in the quarterfinals after losing to her fellow Russian in the French Open final.