The injury will end Richardson's season and leave the Seahawks without one of their leading receivers heading into Sunday's NFC Championship game against the Green Bay Packers in Seattle.
Richardson, a 2014 second-round draft pick out of Colorado, has 271 receiving yards on 29 receptions, the fourth-highest mark among Seattle receivers. He caught one pass for 21 yards Saturday night.
This is not Richardson's first brush with an ACL tear. He suffered the same injury to the same knee during a practice in the 2012 offseason while at Colorado, causing him to miss the entire 2012 campaign.
- Will Green