Olson had an MRI on the ailing joint Monday at UCLA medical center. Although the results were not available by the time head coach Karl Dorrell took the dais at his weekly press conference, Dorrell said the Thousand Oaks High product should miss "weeks."
"In regards to Ben," said Dorrell, "Ben in currently at the hospital finishing up the MRI. We do not have the results yet."
Dorrell said that he did know the injury was a sprain of the MCL.
"He'll probably be out weeks," said Dorrell. "I don't know how many. That will probably be determined after we get the reading from the MRI by the doctors.
"But he will not be available this week. We'll see about his progress."
Olson will be replaced by backup Pat Cowan, who played well in the big lefty's absence at the Rose Bowl Saturday evening.
Cowan completed eight of his first nine passes before finishing 20-of-29 passing for 201 yards and two touchdowns.
"Pat Cowan will be our starter this week," said Dorrell. "Our team will rally around him."
Olson had completed three of his first four passes for 26 yards Saturday when he was hit low by an Arizona defender midway though the first quarter.
His condition is expected to be updated by a UCLA spokesman later in the day.