A nursing supervisor at St. Luke's Hospital in Bethlehem wouldn't provide additional information on the 85-year-old's condition, but The Morning Call of Allentown, Pa., reported Thursday that Bednarik was admitted because of shortness of breath.
"They're still running tests, they still don't know the cause," Ken Safarowic, Bednarik's son-in-law, told the newspaper. "But his heart is as strong as when he was playing, and he is conscious and he just wants to get out of there.
"I'd like to say he's resting comfortably, but I don't know that Chuck can ever rest comfortably. That's just the way he is."
Bednarik played linebacker and center for the Eagles long after the heyday of two-way players. His game-saving tackle helped the Eagles claim the 1960 NFL championship, the last title won by the franchise.
Bednarik was inducted into the Pro Football Hall of Fame in 1967.
The Associated Press contributed to this report.