Senior linebacker Porter Gustin left the Colorado game with a fractured ankle and won’t return this year. (Josh Dunst | Daily Trojan)USC football took a huge blow Sunday when the team announced that senior linebacker Porter Gustin would miss the remainder of the season with a fractured ankle. As the team practiced Wednesday in preparation of Saturday’s road matchup with Utah, Gustin’s absence loomed over the proceedings.Gustin’s seven sacks lead the Pac-12, and the Trojan pass rush has noticeably struggled when he has been out this season. The team is turning to redshirt junior defensive lineman Christian Rector and redshirt freshman linebacker Hunter Echols to fill in for Gustin at the “predator” position. “Replacing [Gustin] is a tough thing to do, but we have to have a next guy up mentality,” Rector said. “We have a good scheme, a good system, so I have to execute it.”No other player on the Trojan defense has more than 1.5 sacks, so the team has big shoes to fill. The pass rush was still excellent when Gustin was injured last season, but that team featured threats like Uchenna Nwosu and Rasheem Green, both of whom have departed for the NFL.Defensive coordinator Clancy Pendergast said there is no replacing a player of Gustin’s caliber. “Everything from work ethic, helping people get lined up during the game, helping to coach the younger guys at practice, to playing and competing at a high level,” Pendergast said. “He’s someone that you can’t replace.”Gustin’s injury comes at possibly the worst time for the Trojans, with the most important game of their season coming up on Saturday. Utah boasts a strong offensive line, with four starters of at least 310 pounds, so USC’s front seven will have its work cut out for it.“They’re very physical up front, they do a nice job in the running game,” Pendergast said. “[Junior Zack] Moss, the running back, is very much a downhill perimeter runner, the [junior] quarterback [Tyler Huntley] is a true dual-threat guy, and they’ve got a lot of speed outside. So they can hurt you in a lot of different ways offensively.” Moss has rushed for 617 yards and seven touchdowns on 110 attempts, averaging 102.8 yards per game and 5.6 yards per carry this season. Huntley is the team’s second-leading rusher, with 207 yards and three touchdowns on 75 attempts.“They’re really physical, their [offensive] line is really big up front,” said freshman linebacker Palaie Gaoteote. “They compact the box and try to run it down your throat.”Utah’s offense is on the rise, putting up 40 or more points in its previous two games against Arizona and Stanford. As Pendergast said, the improvement has been most evident in the run game, as the Utes topped 220 rushing yards in both games.“They’ve gotten themselves in a lot more manageable third down situations, therefore they’re winning on first down,” Pendergast said of the Utes’ recent improvement. “Their offense is very impressive, and it’s a completely different style of offense than what we faced last week in Colorado.”If there’s an area the USC defense can exploit in Utah’s run game, it’s Huntley’s propensity for taking negative plays. The junior signal-caller has 112 negative yards on rushing attempts this season, which the Trojans can take advantage of if they get into the backfield repeatedly like they did against Colorado.Huntley has solid overall numbers in the passing game: He completes 64 percent of his passes for 203.5 yards per game, with seven touchdowns and three interceptions. With Gustin gone, other USC pass rushers will have to contain the speedy Huntley so he can’t make plays outside the pocket. Even so, Helton said the team was focusing on stopping Utah’s run game.“Hopefully, we can do like last game and maybe get up or create third and longs where you’re putting them more in passing situations,” Helton said. “Because when they can lean on that run game, lean on the play-action game, they’re good. That’s right in their backyard.” Utah is notable for its rowdy atmosphere, which the Trojans prepared for this Wednesday by filtering crowd noise during their third down drills. If the practice was any indication, though, the Trojans will struggle to match the energy; the session was quiet, lacking the contentious competitiveness that had characterized the practices over their three-game winning streak.Injury updateHelton said that both Gaoteote and senior linebacker Cam Smith are close to game ready, but neither have been medically cleared yet. Smith is recovering from a hamstring injury, while Gaoteote has not yet cleared concussion protocol.Smith was unavailable after practice, but Gaoteote said he was improving every day and feeling better.The team also pulled redshirt junior offensive guard Jacob Daniel with knee soreness.