Citing a person familiar with Griffin's condition, the newspaper said the rookie signal-caller has a torn lateral collateral ligament and will go under the knife in a matter of days.
The newspaper said doctors will also seek to determine if the rookie signal-caller's anterior cruciate ligament was torn as well.
The Heisman Trophy winner suffered the injury during the fourth quarter of Sunday's NFC wild card round playoff loss to the Seattle Seahawks. He was removed from the game after being helped off the field.
The Post earlier reported magnetic scans performed Monday indicated Griffin had sustained partially torn knee ligaments.
The rehabilitation time from surgery on lateral collateral ligaments can take as long as eight to 12 months, University of Maryland doctor James Dreese told the newspaper.
Redskins Coach Mike Shanahan didn't specify the extent of Griffin's injury during a press conference Monday, saying only he was set to be examined Tuesday by orthopedic surgeon Dr. James Andrews in Florida.