Injury to Shelve Olson at Least Four Weeks

For UCLA, the news Monday evening came in two forms, good and bad.

Quarterback Ben Olson, who injured his left knee against Arizona on Saturday, will not require surgery. But after tests found a tear of the medial collateral ligament, the redshirt sophomore will need at least four weeks to recover.

That leaves him on the sideline for a particularly tough stretch of games during the next month in which the Bruins face Oregon, Notre Dame and California.

While Olson spent Monday afternoon at the hospital undergoing an MRI exam, Coach Karl Dorrell talked about his backup, Patrick Cowan.

“Pat’s proven that he can win because of what he accomplished last week,” Dorrell said of Cowan’s performance off the bench in a 27-7 victory over Arizona at the Rose Bowl.

As a second-stringer, Cowan got only about 30% of the snaps in practice through the early part of the season, but his coach praised him for studying carefully from the sideline.

One of his two touchdown passes against Arizona came on a play that he had not gotten the chance to practice.

“That just shows you right there how he stayed involved in the game planning,” Dorrell said. “Really watching what’s important about his reads and the timing aspects.”

Dorrell said he was so confident in Cowan’s abilities that he wasn’t about to turn conservative when Olson went down early in the game.

Cowan got the green light to throw, especially after some early completions, even if it came at the expense of an effort to develop the running game.

The result was 227 yards passing and only 65 yards rushing.

“I wanted Pat to come out blazing,” Dorrell said. “We thought, ‘We’re not just going to slow down and get his feet wet.’ ”

Osaar Rasshan now becomes the backup, which means coaches might add some twists to the playbook to accommodate a redshirt freshman who, while in high school, ranked among the nation’s top dual-threat quarterbacks.

“We do have to develop a reasonable game plan for Osaar,” Dorrell said. “We’ll have him ready to go in that reserve role.”

Coaches gave some thought to playing Rasshan at the end of the Arizona game, but decided to stick with Cowan.

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The win over Arizona helped UCLA boost some already impressive defensive numbers. The Bruins now rank second in the nation in total defense and rushing defense, surrendering just 221.6 and 50 yards, respectively.

That puts them atop the Pacific 10 Conference in both categories.

Still, those statistics have come against the likes of Rice and Arizona, hardly offensive powerhouses. And the defense suffered a serious hitch against Washington.

“People tend to want to put us down,” cornerback Trey Brown said. “They’re not believers.”

If nothing else, tough games during the next few weeks will give the Bruins a chance to prove themselves. Dorrell called it “a good stretch of the season,” adding, “we’re ready to respond.”

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Dorrell said that Christian Taylor’s sprained ankle was feeling significantly better and the middle linebacker will try to practice this week. Same with defensive tackle Chase Moline, recovering from a back injury.

david.wharton@latimes.com