The 73-year-old actor was seen wearing an oxygen mask when he was rushed by ambulance to the emergency room of a Manhattan hospital, sources told Entertainment Tonight.
Hopper was at NBC headquarters at 30 Rockefeller Plaza earlier Wednesday, as he was scheduled to make a number of NBC appearances, but left after feeling ill.
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Hopper, who was in town to promote his TV series "Crash," was hospitalized after developing flulike symptoms, said his publicist, Sheila Feren.
Hopper was forced to cancel a number of interviews and TV appearances, including "Today" and "Late Night With Jimmy Fallon," where he was replaced by Jack McBrayer of "30 Rock."
The twice-Oscar nominated actor has gotten nods for co-writing "Easy Rider" in 1969 and for his performance in "Hoosiers" in 1986. Hopper's management would not confirm or deny the Entertainment Tonight report but said a statement would soon be issued.