ACL tear ends Steven Mitchell Jr.’s season

USC receiver Steven Mitchell Jr. hobbled to an idling bus Saturday with his left knee cocooned in a bulky brace.

A normal-looking cut on a punt return had buckled Mitchell’s left knee in the second quarter of USC’s 48-14 win over Arizona. He crumpled to the turf without touching a defender.

Mitchell had been in this position before, prior to his freshman season, when he tore the anterior cruciate ligament in his right knee. So he knew the prognosis wasn’t good.

An MRI confirmed those fears on Sunday. Mitchell tore the ACL in his left knee and will miss the remainder of the season.

“Very saddened for him,” USC Coach Clay Helton said during a teleconference with reporters on Sunday. “Unbelievable kid who was really having by far his best season as a Trojan.”

Mitchell’s career has been dotted with injuries, but he “came into this season the healthiest he had ever been,” Helton said.

Mitchell was a steady contributor in a support role as the starting slot receiver. He caught 24 passes this season to compile 226 yards and a touchdown. He led the team in catches against Colorado, with six. Mitchell has a season of eligibility remaining.

In his absence, Deontay Burnett will likely take over the starting role, with part-time quarterback Jalen Greene also pushing for playing time.

Burnett has blossomed this season and has just about surpassed Mitchell’s statistical line: 23 catches for 229 yards and two touchdowns. He caught seven passes against Arizona State, five against Colorado and just one against Arizona, but it was a touchdown reception. Burnett, Helton said, has developed a quick chemistry with quarterback Sam Darnold.

“You don’t see him drop the ball very often,” Helton said. “He’s one of those guys that has unbelievable catch radius. High, low, wherever the ball is, if he touches it, he catches it.”

Helton said he doesn’t anticipate plugging in a freshman receiver into the rotation initially. USC recruited five freshman receivers, but only Michael Pittman Jr. has seen the field. The other four are on track to redshirt, though Helton indicated he wouldn’t be squeamish about sacrificing the season of eligibility if one of the four could help immediately.

“We’re right in contention, we’re one game back right now in the conference standings for the south, and we’ve got to do everything we can to help us move forward,” Helton said. “So if there’s a person that can do that and is a better answer, yes, we’ll use him.”

Too hot?

USC’s offensive linemen were sweating on the bench Saturday afternoon in front of an oversized misting fan. A coach ran through adjustments. A trainer scurried about behind them, squeezing a soaked rag over Zach Banner’s head, draping another one over the neck of Damien Mama.

It was a typical mid-October day in Tucson, with temperatures in the mid-90s. But Arizona plays on field turf, with millions of tiny rubber pellets that radiate heat. The public-address announcer said the field temperature was 137 degrees when the game started, and the ambient temperature only rose from there.

Arizona plays its early-season games during the nighttime to avoid such conditions. Should the Pac-12 have considered moving the start time on Saturday, too?

Helton didn’t think so.

“If it was something that was going to be at risk, I know they would’ve either cancelled the game or move it someplace else,” Helton said.

Last year, five Los Angeles Unified School District schools replaced their fields because the pellets melted under extreme heat. Mike Hovatter, chief facilities executive for the district, told the Times that the fields are supposed to withstand heat up to 180 degrees. But the pellets melted during tests at 140 degrees, close to the game-time temperature in Tucson.

Quick hits

Helton said receiver JuJu Smith-Schuster, who took a helmet to the lower back on Saturday, will return for USC’s next game against California. “Obviously, he’s going to be sore, but with 12 days before the next day he should be fine,” Helton said. … Mama (hyperextended elbow), safety Leon McQuay III (groin, hip flexor) and linebacker Olajuwon Tucker (knee) are not expected to miss time. … With a bye week upcoming, USC will review tape on Monday and practice on Tuesday and Wednesday. USC’s coaches will recruit on Thursday and Friday and the team will begin its game-week preparations for a Thursday night game against California on Saturday.

zach.helfand@latimes.com

Follow Zach Helfand on Twitter @zhelfand