Stephen Colbert, 'Modern Family' cast to guest host 'Good Morning America'

NEW YORK - Stephen Colbert and the cast of "Modern Family" are next up as "Good Morning America" guest hosts for Robin Roberts, who is scheduled to undergo a bone marrow transplant this week.

The surging ABC morning show hasn't missed a beat since Roberts exited on Aug. 30. The co-host has MDS, a blood and bone marrow disease, and is out indefinitely for treatment that includes a transplant of marrow donated by her sister, Sally-Ann Roberts. Robin Roberts had to undergo chemotherapy before the procedure, said Tom Cibrowski, the show's senior executive producer.

Cibrowski offered more details about the schedule of substitutes for Roberts, which is expected to include Oprah Winfrey and newswomen Barbara Walters, Katie Couric and Diane Sawyer sometime next month.

Celebrities will be deployed in much the same way as Jessica Simpson was one day last week, appearing on the pop culture-heavy second hour alongside show regulars George Stephanopoulos, Josh Elliott, Lara Spencer and Amy Robach.

"It shows them in a different light for a little bit and you get to see them do something different," Cibrowski said. "It might be a little funny if they have to read the prompter and there's some slip-up. It's all spontaneous."

The show will feature a different cast member of "Modern Family" each day for a week as the new television season begins. Actor Rob Lowe is also scheduled, Cibrowski said.

While the idea of celebrity guest hosts has been tried before in morning television, ABC's rivals at the "Today" most recently showed its potency when Sarah Palin guested and got strong ratings one day last spring.

With their experience in news, Walters, Sawyers and Couric will work for the full two hours when they come on "Good Morning America" for a day. Each has had extensive morning experience: Walters and Couric on "Today" and Sawyers on "GMA" and a CBS morning show.

"Good Morning America" has consolidated its gains in stunningly fast fashion in a morning television world where loyalties are hard to change. "GMA" beat the "Today" show in the weekly ratings for the first time in 17 years this spring. Except for the weeks that "Today" was in London with the Summer Olympics, "GMA" has won most of this summer. Viewers have punished "Today" for the awkward replacement of Ann Curry by Savannah Guthrie early in the summer.