The redshirt junior will undergo surgery this week and his recovery timeline is 6-10 months. Lake said it's possible Tupuola-Fetui could return at some point during the 2021 season.
Tupuola-Fetui was named a third-team All-American last season despite playing in just four games. He recorded seven sacks and forced three fumbles, emerging as one of the top defenders in the Pac-12.
The edge defender left last Friday's practice early after suffering the injury and didn't attend the Huskies' weekend sessions.
Washington will be hurting at the outside linebacker position this fall, as junior Laiatu Latu was forced to medically retire this offseason due to a neck injury.