Te'o suffered the injury in the opening quarter of the Chargers' 26-22 loss to the Indianapolis Colts while covering running back Frank Gore out in the flat. Te'o went down on his own while trying to plant and cover Gore on a pass route.
Te'o was not touched by another player.
After being looked at by San Diego's training staff, Te'o had to be helped off the field and could not put pressure on his left leg. Te'o was later taken to the locker room on a cart for further evaluation. The Chargers announced he would not return because of an Achilles injury.
Now in his fourth season, Te'o served as the defensive playcaller and is a defensive co-captain for the Chargers. But he's had trouble staying healthy since the Chargers selected him in the second round of the 2013 draft out of Notre Dame.
Te'o, 25, missed 13 games in his first three years because of various foot and ankle ailments. He shed weight during the offseason so that he could play faster and stay healthy during the regular season.
Te'o is the third San Diego player to suffer an Achilles injury this year. Running back Branden Oliver and tight end Jeff Cumberland both suffered Achilles tendon tears and were placed on the season-ending injured reserve list.
Receiver Keenan Allen and running back Danny Woodhead also were lost for the year with ACL knee injuries. Heading into Sunday's contest, the Chargers had 14 players on the team's injured reserve list.