But during her absence from the ABC morning show, she'll be getting a little help from her friends, she said Thursday.
Roberts listed Barbara Walters, Diane Sawyer and Katie Couric among her "wonderful, wonderful friends at ABC News" who will be subbing for her. Others mentioned: talk-show host Kelly Ripa and panelists from the ABC talk show "The View."
Roberts announced last month that she has MDS, a blood and bone marrow disease once known as preleukemia.
On Thursday, she told reporters gathered for the Television Critics Association conference in Beverly Hills, Calif., that her leave would "most likely" start at the end of August or early September.
"It's fascinating-slash-scary how to prepare yourself for something like this," she said, appearing by satellite from ABC's studios in New York. And when asked how she's feeling, she replied, "I do go through moments of fatigue."
But citing the continuing resurgence of "Good Morning America" against its long-dominant NBC rival "Today," she brightened.
"The run that we've had has truly energized me," she said. "It's pretty good medicine, I gotta say, to be taking!"
In particular, ABC was crowing Thursday that, for the first time in 17 years, "GMA" had seized first place among total viewers (almost 4.6 million vs. 4.25 million for "Today") as well as tying "Today" for first place in the 25- to 54-year-old demographic, each with 1.74 million.
ABC News President Ben Sherwood was inspired to frame the victory in Olympic terms.
"For 852 straight (weekly) races, the 'Today' show won the gold medal, going back to 1995," he said. Then, several weeks ago, "GMA" snapped the "Today" winning streak, "and stood there alone for the first time in 16 years to get its own gold medal."
"And after 879 weeks running behind in younger viewers, 25-to-54," Sherwood went on, "GMA" is "standing there at the gold-medal podium, unbelievably in an actual statistical tie with the previous champs."
Meanwhile, Sherwood acknowledged a mistake ABC News made last week during coverage of the movie theater shooting in Aurora, Colo., that killed 12 people and injured dozens more.
ABC News Chief Investigative Correspondent Brian Ross speculated on the air about the political ties of the alleged gunman, James Holmes, erroneously identifying him as a member of the tea party.
"It was a mistake," Sherwood said. "We recognized it immediately. We owned it immediately. We corrected it immediately. We apologized for it."
Declaring, "That particular moment didn't live up to the standards and practices of ABC News," he said, "I take responsibility for it. The news division knows how displeased I am about it. And we will do everything we can to prevent it ever happening again."