Robin Roberts

Good Morning America's Robin Roberts will begin medical leave to have a bone marrow transplant at the end of this week, she announced Monday.

Roberts, 51, said on-air that her last day before an extended absence will be Friday. She plans to check into the hospital next Tuesday to begin preparing for the transplant, which will occur several days later. Her sister Sally-Ann Roberts will be the donor.

Throughout the week, Good Morning America will air segments celebrating "Robin's Journey."

Robin Roberts has rare blood disorder, will have bone marrow transplant

In June, Roberts, a breast cancer survivor, announced that she had been diagnosed with myelodysplastic syndrome (also known as preleukemia), a blood and bone marrow disease.

Among the guest hosts who will fill in for Roberts in her absence are Diane Sawyer, Katie Couric and Barbara Walters. Roberts plans to return to GMA after her recovery, though a specific date has not been set.