Navy safety Kwazel Bertrand had two fumble recoveries and assisted on a pair of goal-line stops vs. Air Force before he suffered a broken ankle. (Jonathan Newton/The Washington Post)

When Navy safety Kwazel Bertrand was carted off the field during the fourth quarter of a 33-11 victory over Air Force on Saturday, Coach Ken Niumatalolo feared the worst.

Two days later, the senior had surgery to repair a broken ankle, and at practice Tuesday afternoon, Niumatalolo confirmed that Bertrand is out probably for the rest of the season.

The best-case scenario would be for Bertrand to play against on Army Dec. 12 in the final regular season game, but Niumatalolo conceded that would be a long shot.

Bertrand’s absence places the secondary in a precarious position entering this weekend’s game against 15th-ranked Notre Dame in South Bend, Ind. The four-year starter was coming off one of the finest performances of his career in the first leg of the Commander-in-Chief’s Trophy series with two fumble recoveries and assists on a pair of goal-line stops.

“It’s sad, first from the standpoint that this kid worked so hard,” Niumatalolo said. “He had a really good game, probably his best game. Big emphasis for us in that game was not to get any balls thrown over our heads, and he was on point. We just told him, ‘Hey, I guess the one silver lining is you helped us beat them, and if it wasn’t for you, who knows? We may not beat those guys.’ ”

Junior Daiquan Thomasson is next on the depth chart at rover. Thomasson has played sparingly in three games this season, including replacing Bertrand for the final minutes against Air Force. His only playing time last year came in four games on special teams, but Thompson is among the best athletes on the roster, according to Niumatalolo.

Navy’s secondary remains one of the defense’s most experienced units, particularly at cornerback with senior Quincy Adams and junior Brendon Clements. Senior Lorentez Barbour is the other starting safety. Cornerbacks Elijah Merchant, a sophomore, and Sean Williams, a freshman, also have started one game each this year. Niumatalolo indicated Williams could move to safety if needed.

The defensive backfield is preparing for what figures to be its most daunting individual test of the year in Fighting Irish wide receiver Will Fuller. The junior leads Notre Dame in average per catch (20.5 yards) and touchdown receptions (six) and is a major reason why the Fighting Irish are ranked 14th in the country in scoring offense (37.2 points per game).

Fuller was named Notre Dame’s offensive player of the year last season after logging 76 receptions for 1,094 yards and 15 touchdowns, third most in the Football Bowl Subdivision. He had three catches for 16 yards and one touchdown in last year’s 49-39 win against Navy at FedEx Field.

“We lost not only a great player but a great leader of our defense,” Navy nose tackle Bernie Sarra said of Bertrand. “Kwaz was one of the great upholders of our standard. He understood what it took to win. He was a winner, had a ton of reps. Daiquan has a big challenge to step up. It’ll bring the best out of Daiquan and hopefully the best out of the secondary and also the best out of the defense.”

Sarra, meantime, is practicing this week with a hard cast covering his right forearm, wrist and hand. The senior co-captain said he suffered a minor injury against Air Force but has no doubt he will be on the field to face Notre Dame.

Navy, which is 4-0 for the first time since 2004, has lost four straight to the Fighting Irish (4-1) in the longest continuous intersectional rivalry in college football. The Midshipmen have allowed an average of nearly 49 points in those losses.

“This is our best defense that we’ve had, and we’ll go in there and take a shot at them,” Niumatalolo said. “Like I said, they’re really good, always have been. Coach [Brian] Kelly, I’ve always admired the way he calls plays. If he sees something, he’s going to exploit it. He’s got a great feel for the game, so we’ve got to be able to adjust. We’ve got some ideas on what to do, but he’s going to adjust really quickly to us.”