After a successful switch from linebacker to tailback, Tre Madden's 2012 season ended before it even had a chance to begin last week.
While the Trojans are viewed as one of the nation's top teams heading into the fall, the loss of Madden will be a tough one to stomach seeing as USC only has three running backs on scholarship.
In light of Madden's injury, let's take a look at five players the Trojans can not afford to lose if they hope to make a run at the national title in 2012...
Placing Barkley at the top of this list is a no-brainer. The rising senior quarterback is the heart and soul of USC's team and losing him for any stretch of the season would be devastating to the Trojans' title chances.
While Lane Kiffin does have gifted youngsters Max Wittek and Cody Kessler waiting in the wings, both are just redshirt freshmen and have yet to throw a pass at the collegiate level.
Barkley brings more than just his throwing ability to the quarterback position. His experience and leadership ability have been instrumental in rallying USC through a two-year bowl ban and back atop the national stage.
While Kessler and Wittek have shown flashes of brilliance during practices, Matt Barkley is an irreplaceable presence on the field for the Trojans.
The Heisman hopeful played nearly every minute of every game for USC a year ago and Kiffin should be hoping for more of the same if he wants to see his team in the national title discussion.
Like Barkley on offense, Robey is one of the leaders of the USC defense.
Since he arrived on campus, the Frostproof, Fla. native has earned his keep by shutting down the opponent's star receiver. Robey's presence was a big reason why USC's secondary still played strong despite serious depth issues at the cornerback position.
This spring, USC has newfound depth at the cornerback spot now that Torin Harris and Anthony Brown are back from injury. The duo of Brian Baucham and Ryan Henderson should also provide extra insurance at the position.
However, none of these other cornerbacks on USC's roster have displayed the shutdown ability that Robey has.
With Robey out, opposing quarterbacks would have a field day attacking the Trojans' talented yet inexperienced cornerbacks.
Robey has been durable throughout his USC career and the Trojans better hope that doesn't change in 2012.
Make no mistake, Heidari plays one of the most important pieces in USC's national championship aspirations. As a true freshman in 2011, Heidari hit 15 of his 17 field goal tries and all 50 of his extra-point attempts.
The rising sophomore was on numerous freshman All-America lists and also earned All-Pac-12 first team honors for his efforts a year ago.
Heidari's longest field goal in 2011 was 50 yards against Stanford and the freshman was successful on four out of five kicks from 40 yards and deeper.
Heidari was as clutch as they come for USC a year ago and if you pair him with punter Kyle Negrete, you're looking at one of the best special teams duos in the entire country.
The Trojans certainly had an edge late in games with Heidari on their sideline so losing him in 2012 would potentially be devastating to USC's BCS bid.
USC's tailback depth, or lack thereof, took a serious hit with Tre Madden's season-ending knee injury.
Now with only three scholarship tailbacks on the roster, it is imperative that McNeal stay healthy throughout the entire season.
McNeal stands just 5'7", 190 lbs, but he packs a lot of punch into his small frame. The rising senior rushed for 1,005 yards in 2011 after assuming the feature back duties midway through the year.
Should McNeal go down, the injury-prone duo of D.J. Morgan and Buck Allen would be next in line to step in.
While Morgan looked solid in the early goings of 2011, fumble problems ultimately landed him a spot on the bench and the speedy sophomore was unable to climb out of Coach Kiffin's doghouse.
Javorious "Buck" Allen redshirted in 2011 and has yet to register his first carry at the college level.
While Kiffin may still opt to mix things up by giving incoming freshman Nelson Agholor or redshirt freshman fullback Soma Vainuku looks at running back, as of right now depth issues are a serious concern for USC.
If the Trojans are to make it to the promised land this fall, they will need a healthy Curtis McNeal to lead them on their way.
No disrespect to Robert Woods, but Marqise Lee is the wide receiver USC must keep healthy in 2012 if it is to have any shot at a trip to Miami in January.
Lee played in all 12 games as a true freshman for USC and seemed to make a tremendous impact in each of them.
On the season Lee racked up 1,143 yards and 11 touchdowns on his way to earning All-Pac-12 second team honors.
Lee was instrumental in the Trojans' victory over Oregon, catching eight balls for 187 yards and a score in USC's 38-35 upset in Eugene.
While Woods spent much of 2011 batting lingering shoulder and ankle injuries, it was Lee who rose to the occasion and willed USC down the stretch.
Luckily for USC fans, it appears Matt Barkley will have both Lee and Woods at his disposal in the fall once Woods fully recovers from the ankle surgery that is keeping him out of spring practice.
However, if for some reason the durable Lee is unable to go, the pressure will rest squarely on the shoulders of an otherwise fragile wide receiving corp that may not be able to handle the extra burden.