Entertainment Tonight ET Online ETOnline.com

Good Morning America's Robin Roberts bid farewell to co-workers and viewers on Thursday -- her last day on the show before an extended medical leave of absence to undergo a bone marrow transplant.

During the broadcast, Roberts thanked co-anchors George Stephanopoulos, Josh Elliott, Sam Champion and Lara Spencer for their continuing support and promised to return to GMA as soon as possible. "You are going to keep the spirit going," she told them, adding that she'll be "watching you in my jammies."

RELATED: Oprah to Fill in For Robin Roberts on GMA

Stephanopoulos praised Roberts for being so open about sharing details about her illness -- the rare blood and bone marrow disorder Myelodysplastic syndrome (MDS) -- in a bid to educate others. "We are there for you Robin, and we will be every day," he said.

Roberts announced in June that she had been diagnosed with MDS after successfully fighting breast cancer. She is scheduled to be admitted to the hospital next Tuesday and approximately 10 days later will receive a bone marrow transplant from her sister. Among those to fill in for Roberts during her absence include Oprah Winfrey, Diane Sawyer, Katie Couric, Barbara Walters, Elizabeth Vargas, Chris Rock, Rob Lowe and the cast of Modern Family.

RELATED: Celebs Tweet Support for Robin Roberts

The 51-year-old host was originally scheduled to stay on GMA through Friday, but announced she was leaving a day early so she could visit her ailing mother and other family members who live in areas of Mississippi affected by Hurricane Isaac. "Our beloved mother, the matriarch of our family, 88-years-old, has had some health issues recently and it's got to the point that (her sister) Sally-Ann and I need to get home."

Roberts' sister and doctor also appeared on Thursday's show as part of extensive GMA reporting on the disease and treatment that has included uplifting stories about families who have faced and overcome an MDS diagnosis.

RELATED: Robin Roberts Going on Medical Leave