Belgian world number two Justine Henin-Hardenne has pulled out of next week's Linz tournament in Austria, the WTA said on Saturday.
Henin-Hardenne, who beat Russian Vera Zvonareva to reach the semi-finals of the Swisscom Challenge in Zurich and could seal the number one spot if she wins the tournament, said she was tired after a gruelling run of matches.
"Unfortunately I have no option but to rest after this week to ensure I will be 100 percent for the WTA championships in three week's time," said Henin-Hardenne, who has played in 17 tournaments this season.
"It is going to take everything I have just to survive this week in Zurich. Physically I am feeling very tired now. It is the end of the season and all players are in the same situation.
"Since the US Open I have been feeling more and more physically and mentally tired and it has got to the point where I just have to take a break from playing.
"But I am very disappointed for the tournament and fans in Linz," the 21-year-old added.
The French and US Open champion missed out on the chance to go top of the rankings when she lost to world number one Kim Clijsters in the final of the Filderstadt Grand Prix in Germany last week, but could overtake her compatriot if the two meet in the final in Zurich on Monday.
But Henin-Hardenne said she did not want to burn out in an effort to reach the number one spot.
"I am not thinking about this," she said. "It didn't help me in Filderstadt so it is not in my mind to be number one after this tournament. Everyone is talking about it but it does not help me.
"It is a goal in my career, to be number one, but lots of things have happened in the last few months so I just have to take my time."