Stephens had not played since a Dec. 3 91-60 win against Austin Peay.
"I don't expect he'll be able to go for the rest of the year," Pastner said. "His knee has been bothering him. We'll have to get with the trainer. He just is not able to practice right now."
Pastner said he will explore the possibility of getting Stephens a medical red shirt, which would preserve one year of playing eligibility.
"It's up to the doctors and all that," Pastner said. "He just can't practice. Going into the game against Murray State, I was counting on him and he came up and told our trainer, ‘I can't even jump.'
"They're going to get it checked out and see what it is. Hopefully it's just tendonitis but obviously, for DJ, who's an athlete and plays above the rim like he does, it's hard for him when you're having that type of pain."
Stephens is averaging 1.3 points per game and one rebound. He was mostly utilized as a spark off the bench for Memphis, which dropped a home contest to unranked Murray State on Sunday, 76-72.
"As of right now, his knees are such that he can't even practice or jump," Pastner said. "He can barely touch the rim right now. Obviously, without his athleticism, he doesn't help us."