The funnywoman was due to join her A League of Their Own co-star onstage for a question-and-answer session at the Paris Theatre in Manhattan ahead of a screening of new concert movie Madonna: The MDNA Tour.
However, O'Donnell pulled out at the last minute after receiving a phone call from doctors, leaving Madonna to host the event on her own.
O'Donnell's spokesperson tells the New York Post's gossip column Page Six, "Rosie had a suspicious Cat (computer assisted tomography) scan (that had to be) checked out," and adds that the star was "given a clean bill of health" on Wednesday (19Jun13) morning.
The funnywoman has not released any further information about her scare. The 51 year old suffered a heart attack last August (12) and subsequently lost 12 pounds (5.4 kilograms) after revamping her diet.