Robin Roberts Credit: Ida Mae Astute/ABC via Getty Images

Robin Roberts is ready to do battle.

On Monday, the 51-year-old Good Morning America co-anchor announced that her extended medical leave begins next Monday, Sept. 3; recently diagnosed with myelodysplastic syndrome (MDS), a rare blood and bone marrow disorder, Roberts is undergoing a bone marrow transplant in September, and she'll temporarily sign off this Friday Aug. 31.

With an ongoing feature called "Robin's Journey," this week's GMA will put a spotlight on Roberts' treatment, procedure and recovering process, with her medical team weighing in her fight against MDS -- and other families who have dealt with the disease.

"It still takes about 10 days after being admitted because there are some things you have to go through before the (bone marrow) transplant actually occurs," said Roberts, whose sister, Sally, will be her donor.

Roberts took a trip to the Vatican in Rome, Italy - where she visited a special altar and prayed "for all those who have prayed for me," she tweeted to her fans.