Serena Williams withdrew from the Dubai tournament. (Julian Finney / Getty Images)

Just days after becoming the oldest player to be ranked No. 1 in the world, Serena Williams has withdrawn from the Dubai Championships because of a lower back injury.

Williams took the No. 1 ranking for the sixth time in her career on Friday, although she lost to Victoria Azarenka, the No. 2-ranked player, in Qatar on Sunday. Azarenka also dropped out of the Dubai tournament, saying she has a bone bruise in her foot.

Williams, 31, has been battling injuries of late, but won Wimbledon, the U.S. Open and an Olympic gold medal last year. Williams was dealing with back and ankle injuries when she lost an Australian Open quarterfinal last month to Sloane Stephens.

Chris Evert formerly held the distinction of being the oldest top-ranked player. She was just under 31 in 1985. Martina Navratilova also was shy of 30 she last held the top spot. Steffi Graf was 27.

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