Senior outside linebacker, team captain and sack leader Porter Gustin suffered a fracture in his right ankle that will end his senior season and USC career, a huge blow for USC's defense in the aftermath of Saturday's 31-20 win over No. 19 Colorado. USCFootball.com reporter Shotgun Spratling was the first to report a significant injury to Gustin early Sunday morning and it was confirmed by head coach Clay Helton in his Sunday media call.

"That will take him out for the rest of the season," said Helton bluntly. "He will have surgery this week."

Helton said the injury – which has as 3-to-4 month rehab – occurred on the final defensive drive of the game with less than 2:30 left in the game, when Gustin got caught up with two blockers. His career ends with Gustin has 137 career tackles, 21 sacks and 33 tackles for a loss.

"I had a chance to be with him when we saw the x-ray last night after the game," said Helton, who added that the team was numb."It's extremely hard because he's put so much into it....now it's about him going through surgery and him getting well."

The loss will be significant: Gustin has been USC's most consistent and best pass rusher this season, currently leading the team with seven sacks. By comparison the rest of the team has six combined sacks and defensive lineman Malik Dorton is second with 1.5 sacks. Gustin is also tied for second on the team with 28 total tackles and a team-high 10 TFL.

"He's definitely an x-factor. He does a great job in the run game. He's very stout in the run game. Does a great job creating his pass rush and it's just really great to have a guy like that, who is mature, who has been doing it for a good amount of time that can also help the other young guys when he's in there with them," said defensive line coach Kenechi Udeze after the Colorado win. "I mean it goes further than just in the game. On the practice field, he does an amazing job helping other guys and making sure they are always in the right position and doing what they are supposed to do."

Gustin left the game late in the second half, removed his cleat and headed into the medical tent. He wouldn't leave the Coliseum until more than an hour after the game had ended, his foot in a boot. That appears to be aided by an embarrassing situation for USC where it left Gustin in the middle of the field after the game without any way of getting off.

Gustin's ankle fracture is the fourth major injury he's suffered over the last two seasons; he entered this season after an injury-riddled junior campaign, limited to just four games as he battled a fractured toe and a torn bicep, injuries he suffered against Stanford and Texas, respectively. He famously played against the Longhorns, just days after he received toe surgery, recording two huge sacks in the first half before being pulled. He made a brief return against ASU but that was his final time suiting up in 2017. He finished the year with 16 total tackles, three sacks and three TFL. He also suffered a torn meniscus in fall training camp, although he made it back in time for the season opener against UNLV. Gustin, who has 1.5 sacks against Colorado, was just getting back from an ankle impingement that he suffered in USC's 24-20 win over Arizona before the bye week.

USC, which played without senior Cameron Smith (hamstring) at middle linebacker on Saturday, will look to redshirt freshman Hunter Echols or Christian Rector, who filled in for Gustin last season. There is also promising freshman Kana'i Mauga, who picked up first teams reps in the spring and fall. The Trojans go on the road to Utah this weekend.