Roberts, 51, left "GMA" on medical leave Aug. 30. The breast-cancer survivor has myelodysplastic syndrome, a blood condition formerly called pre-leukemia, but her treatment was temporarily postponed when her 88-year-old mother died.
"The start of last week went well, but the daily chemo/treatment caught up to me by the weekend," People.com reported Roberts wrote in her blog Tuesday. "My body is so weak, but not my mind. YOU give me the courage to keep going."