BOISE - The injury news keeps getting worse for Boise State and its highly ranked defense.

Coach Chris Petersen confirmed that senior nose tackle Mike Atkinson will miss the rest of the season after tearing an ACL in Saturday's 21-19 loss at home against San Diego State.

All season, Atkinson has been one of the on-field leaders and a consistent and disruptive force for a defense that is very young up front. His 37 tackles rank sixth on the team and he has two forced fumbles and one interception return for a touchdown, the only score in Boise State's 7-6 win over BYU back in September.

"I still think we've got a good core of defensive lineman," Petersen said. "You lose a guy for the season whenever it is, that's hard. He's a good tough, true nose tackle, and those guys are hard to find."

Ricky Tjong-A-Tjoe, who has played extensively at tackle this season, is projected to take over at nose tackle, while Darrin Koontz will move into the void at tackle when Boise State (7-2, 4-1 Mountain West) plays at Hawaii on Saturday.

The setback is just the latest blow for a defense already hobbled by medical and disciplinary problems. Starting safety Lee Hightower is on track for missing a third straight game for violating team rules. Petersen did not address the status of Hightower during his regular meeting with reporters Monday.

Defensive tackle Greg Grimes and nickel Dextrell Simmons are questionable, though Simmons is listed as the starter on the depth chart.

Despite the injury woes, the defense kept the Broncos close in Saturday's rare home loss. Petersen cited some costly penalties and missed tackles that kept alive San Diego State scoring drives. But the Aztecs only gained 269 yards on offense and two of their three touchdowns were directly attributable to poor special teams by the Broncos. The Aztecs returned the opening kick for a touchdown then a blocked punt in the third quarter set up the San Diego State offense at the Broncos 8-yard line.

The Boise State offense didn't help much, either. After a productive first half, the Broncos gained only 26 yards in the third quarter before scoring on their only possession in the fourth quarter to pull within 21-19.

The defeat marked the second year in a row that a November loss at home cost Boise State its lock on the conference title and shot in a BCS game. Coming into the game, Boise State had a 71-1 record in Bronco Stadium dating back to Sept. 22, 2001.

"We don't lose too much around here," said senior receiver Chris Potter. "When it does happen, people seem to kind of hang onto it a little longer. In the locker room, especially in the past, we've had to learn that next Saturday comes around quick.