Hingis underwent medical tests after losing 7-5 6-4 to Spain's Conchita Martinez in their German Open semifinal on Saturday and accepted she should take a rest, German Open organisers said on Sunday.

Four-times Italian Open champion Martinez also pulled out of the Rome event because of an Achilles tendon injury she aggravated while playing doubles in Berlin on Saturday.

Martinez was playing South African Amanda Coetzer in the German Open singles final on Sunday.

Hingis's injury was not serious and should not threaten her participation in the French Open starting on May 29.

"I have played a lot of tennis in the past two weeks and my foot was bothering me last week in Hamburg also," Hingis said in a statement released on Sunday.

"I had an x-ray and the doctor told me that I would have to rest my foot for a week or so. My main goal is to be 100 percent fit for the French."

The 19-year-old Swiss will lose the number one spot to Lindsay Davenport when the new rankings are released on Monday.