NEW YORK (AP) -- Robin Roberts says Friday will be her last day co-anchoring "Good Morning America" for a while.

On Monday's edition of the ABC News wakeup program, Roberts made official the start date for what's being called her "extended medical leave."

Roberts told viewers in July that she has MDS, a blood and bone marrow disease once known as preleukemia.

She says she will be hospitalized next week to prepare for the bone marrow transplant that will take place about 10 days after that.

But looking further ahead, Roberts noted she is luckier than many workers who become ill. She says her bosses have been generous in giving her the needed time off, and her job is waiting for her when she's well enough to return. She described herself as "very blessed."