Country singer Martina McBride sang for Roberts in the ABC morning news show's New York studio and fellow anchors presented her with pajamas and a book of well-wishes.

"I will be back, you know," Roberts said. "This is just, 'See you later. See you soon.' I will get back as fast as I can."

Roberts, 51, revealed in June that she had been diagnosed with myelodysplastic syndrome - a disorder triggered by her treatment for breast cancer five years ago. Her older sister, Sally-Ann, will be the bone marrow donor.

Roberts was due to start her medical leave on Friday but she said she was leaving "Good Morning America" a day early in order to spend time with her mother, who has health issues.

Producers said on Thursday that Oprah Winfrey, comedian Chris Rock and the cast of TV comedy "Modern Family" will help fill Roberts' shoes during her leave, along with ABC News stars like Diane Sawyer, Katie Couric, Barbara Walters and Kelly Ripa.

(Reporting by Jill Serjeant in Los Angeles; editing by Bob Tourtellotte and Matthew Lewis)

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