Petersen said McClatcher was set to meet with the team's medical staff to discuss treatment options and that he expects the junior to undergo surgery.
Because the injury occurred in the fourth game of the season, Petersen said he expects McClatcher to qualify for a medical redshirt.
The injury occurred in the Huskies' 37-10 win at Colorado on Saturday.
McClatcher ranks second on the team with 10 catches for 128 yards. After finishing third on the team with 31 catches for 574 yards last season, he figured to play a significant role in an offense that is replacing John Ross, a first-round pick in the NFL draft. McClatcher made eight catches for 78 yards as a true freshman in 2015.
No. 6 Washington (4-0, 1-0 Pac-12) travels to Oregon State (1-3, 0-1) on Saturday.