Roland Garros officials said on Monday that a female player in the qualifying competition had tested positive for Covid-19 and withdrawn.
"In line with the tournament's health protocol, the player has been withdrawn from the women's singles and has been withdrawn from the singles qualifying draw," said a statement without naming the player but explaining she would quarantine for seven days.
Five other players suffered the same fate the day before, organisers said.
Men's qualifying began on Monday while the women start on Tuesday, trying to earn a place in the rescheduled clay-court major which runs from September 27 to October 11.
"In total, about 900 tests have been carried out since Thursday," tournament officials said.
Tournament director Guy Forget said earlier in September that players would be tested "upon their arrival and will receive their accreditation as soon as the first negative test is returned."
A second test will be carried out within 72 hours and then another every five days based on a player's progression in the tournament, he said.
Organisers hope to welcome back fans but have reduced the planned daily attendance from 20,000 to 5,000.