Harrington was the third player selected in the 2002 draft and spent four seasons with Detroit before brief tenures in Miami, Atlanta and New Orleans.
New Orleans signed Sean Ryan to replace Shockey, who will be out of action for at least three weeks with a sports hernia. The Saints had to free up a roster spot to make room for Ryan and Harrington was considered expendable.
Harrington has played in 81 games and thrown for 14,693 yards with 79 touchdowns and 85 interceptions.
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