Granger, a 6-foot-2-inch, 302-pound junior from Dallas, was hurt late in the second quarter of the second-ranked Sooners' 55-14 victory at Washington last Saturday.
No specifics were disclosed but officials said he will be sidelined at least the next four weeks.
"There's something in the tendon and the bone and they (Oklahoma physicians) are experimenting on whether to let it heal or take four weeks and see if DeMarcus can come back, or the other thing is to possibly do surgery and pin it," Oklahoma Coach Bob Stoops told The Norman (Okla.) Transcript newspaper following Wednesday's practice.
Granger made six tackles in the Sooners' first three games and had made a promising recovery from a preseason back injury. He wasn't a starter when the season started but became part of a four-man rotation.