Coach Bronco Mendenhall made the announcement after practice Tuesday.
The 6-foot-3, 230-pound redshirt freshman was running a route when he dropped to the turf untouched. He's scheduled to have surgery on his right knee.
Mendenhall says Richards was No. 1 on the depth chart among traditional tight ends on the roster. The Cougars also employ sets that use more pass-catching tight ends that get flexed out wide away from the offensive line.
Quarterback Taysom Hill is confident in the depth at the positon and says he doesn't expect any scheme changes due to the injury.