"I'm very sad I have to withdraw from the tournament, it was impossible to continue the tournament because a left abdominal injury," Halep said. "I have great memories from Rome last year when I reached the semifinal.
"I will fly home to Bucharest tomorrow and I will have treatment every day. I hope the treatment, together with a few days of rest, will allow me to start practice again next week and I hope I will be ready to play Roland Garros."
Halep is projected to overtake Victoria Azarenka and move to a career-high ranking of World No.4 when Monday's rankings are released.
Those same rankings will be used to determine this year's Roland Garros seeds.