Robin Roberts, the "Good Morning America" co-anchor who has been out on sick leave will not be returning to the show until May or June.

Roberts, 52, reportedly has "extremely weak" immune system so doctors are holding off on her returning to work for another "5 or 6 months," sources told TMZ.

ABC executives had hoped that Roberts would return to her seat next to Josh Elliott, Lara Spencer and George Stephanopolous in February as they believe that she would help boost even more ratings.

Roberts is in recovery from receiving chemotherapy and a bone marrow transplant in October. She had been diagnosed with myelodysplastic syndrome, a rare blood disorder in June. She took a leave of absence in late August and underwent the surgery thanks to her sister, Sally-Ann Roberts who was her bone marrow donor.

Roberts' progress is going very well and her progress has been documented on the leading popular morning show. She appeared on a segment earlier this month to share her recovery.

Many guest celebrities have appeared on the show to temporarily fill in for the anchor - Jessica Simpson, Katie Couric, Oprah Winfrey, Diane Sawyer, Barbara Walters, Rob Lowe, Stephen Colbert and the cast of "Modern Family" are just a few that have graciously sat in for the morning show host.