Li Na reached the semifinals of the WTA Championships with a 6-2, 6-1 victory Friday over Victoria Azarenka, who was wincing in pain from a back injury that brought her to tears.
Rafael Nadal is guaranteed to supplant Novak Djokovic atop the rankings after advancing Saturday to the final of the China Open when Tomas Berdych of the Czech Republic retired due to an injury.
Bernard Tomic advanced to the second round of the Thailand Open when Ivo Karlovic retired with a back injury while trailing 6-7 (3), 6-4, 4-2 on Tuesday.
Wimbledon champion Andy Murray will have surgery on a long-standing back problem and miss the rest of the season.
Ayumi Morita of Japan pulled out of the U.S. Open on Sunday because of a lower back injury.
Don't count out Venus Williams for a U.S. Open appearance.
Venus Williams has pulled out of World TeamTennis matches next week because of the back injury that kept her out of Wimbledon.
Venus Williams announced Tuesday that she is skipping Wimbledon because of back problems.
Andy Murray is set to make his return from a back injury in next week's grass-court tournament at Queen's Club in London.
Venus Williams lost a marathon first-round match to Poland's Urszula Radwanska at the French Open, leaving questions about her ongoing back injury and her future in her wake.
Andy Murray withdrew from the French Open on Tuesday because of a chronic back injury and will now focus on preparing for the start of the grass-court season next month.
Three-time champion Venus Williams has withdrawn from the Sony Open because of a lower back injury shortly before her third-round match against fellow American Sloane Stephens.
Serena Williams has withdrawn from the Dubai Championships because of a lower back injury.
Defending champion Agnieszka Radwanska led several of the top seeds into the Dubai Championships quarterfinals on a Wednesday overshadowed by the withdrawal of Serena Williams because of a back injury.
Venus Williams has withdrawn from next week's Qatar Open due to an ongoing lower back injury.
Venus Williams has pulled out of next week's Open GDF Suez tournament and the upcoming Fed Cup against Italy because of a back injury.