Harrington, 32, was taken to a hospital with injuries that were not life-threatening, police told The Oregonian.
A Toyota RAV4 struck Harrington's rear bicycle wheel from behind at 8:24 p.m. Sunday, police said.
Driver Derek Johnston, 26, stayed at the scene and cooperated with police. He was cited for following too close.
Harrington was a star quarterback for the University of Oregon and played for the Detroit Lions and other NFL teams from 2002 to 2009. He is now a radio analyst for Fox Sports in Portland