San Diego Chargers coach Mike McCoy confirmed that wide receiver Keenan Allen suffered a torn ACL during Sunday's 33-27 overtime loss to the Kansas City Chiefs.
The Chargers will fill the open spot by activating Joey Bosa from a roster exemption after the first-round pick missed most of the preseason because of a contract dispute.
Allen immediately grabbed for his right knee after falling to the turf while trying to make a cut in the middle of the Arrowhead Stadium field late in the second quarter of Sunday's game against the Chiefs.
While he was bumped by the Chiefs defender, the injury was essentially non-contact and he was carted off the field, clearly distraught and with his hand over his face.
Despite missing half of the 2015 season with a lacerated kidney, Allen still caught 67 passes for 725 yards and four touchdowns.
Without him in the lineup for the second half on Sunday, the Chargers blew a 24-3 lead.
While running back Danny Woodhead led the Chargers in receptions last year and tight end Antonio Gates was third on the team, behind Allen, Stevie Johnson's 45 receptions were fourth and Dontrelle Inman was next among receivers with 35 catches.
Johnson is lost for the season after suffering a meniscus injury last month.
Allen's injury will put more pressure on both Inman and free-agent acquisition Travis Benjamin to make plays for veteran quarterback Philip Rivers.
Benjamin had a team-high seven receptions in the loss to the Chiefs, but for only 32 yards.
Second-year receiver Tyrell Williams led the team with 71 yards on just two receptions.