Hingis said she did n't think she had the appetite for the training that would be necessary .
Hingis won five Grand Slam singles titles and nine in doubles and was ranked number one in the world for a total of 209 weeks .
Hingis , who won five Grand Slam singles titles and nine in doubles and was ranked number one in the world for a total of 209 weeks , said she did n't think she had the appetite for the training that would be necessary .