Whittingham called the injury "very strange" while discussing it with reporters after Utah's 32-25 win over Oregon on Saturday. The coach said Moss' knee "locked up on him" when he was getting into bed.
"It could have been a week ago, a month ago, a year ago," Whittingham told reporters of Moss' original injury. "There's just no way to tell."
Previous reports had indicated that Moss suffered the injury during practice Wednesday.
No timeline was given on Moss' return, with reports this week saying his season was over. Whittingham also noted that the running back may have played his final game for Utah.
With 1,092 rushing yards and 11 touchdowns this season, Moss had been on pace to break Utah's single-season rushing record (1,519 yards).
In Moss' absence, Armand Shyne led the Utes with 174 rushing yards on 26 carries in the victory over Oregon.
Moss has 2,647 career rushing yards and 23 touchdowns on 477 carries. He would be a candidate to enter the NFL draft, or he could return to Utah for a final season in 2019.
Information from ESPN's Adam Rittenberg was used in this report.