LOS ANGELES >> The nightmare scenario for USC next season is a lengthy injury to star quarterback Sam Darnold.

But a trickier question for the Trojans is what they do if Darnold suffers a sprained ankle or some other injury that only keeps him out for a limited amount of time? Imagine in Game 2 against Stanford at the Coliseum, if Darnold leaves the game in the second quarter and does not return.

For USC coach Clay Helton, there are three options: He can use redshirt freshman Matt Fink, who is unproven but targeted to be the backup next season. He can insert highly regarded true freshman Jack Sears and burn his redshirt year. Or he can move wide receiver Jalen Greene back to quarterback.

No one might admit it right now, but Greene is currently the best quarterback of the bunch. He knows the offense, is the most athletic and possesses a strong arm. But Greene said Tuesday he wants to play wide receiver. Would Helton risk tossing him into a game at quarterback without practice time?

That leaves Fink and Sears. Between the two, Sears is the quarterback of the future. But he might be on the scout team next season and it could be too much for the normally cautious Helton to burn a redshirt and play a true freshman that early in the season.

So Fink is the safe choice. But how long would Helton be willing to go with him? Game 3 would be against Texas. Then back-to-back road games against California and Washington State, with a short week to play the Cougars because the game is on a Friday.

That’s not conducive to going with the backup if you don’t envision him as a long-term choice.

“Whoever the backup is, the question is what is he?” USC offensive coordinator Tee Martin said. “What do we become with him? What does our offense become?”

The caveat in all this is Greene could switch at any time but that wouldn’t help with a sudden injury to Darnold, who it should be noted is extremely elusive, which made it hard for defenses to hit him last year.

“We’re going to focus (Greene) at wideout,” Helton said. “We lost Darreus (Rodgers) and JuJu (Smith-Schuster). We also lost some backups too (Isaac Whitney, DeQuan Hampton).

“We’re going to try to prep Matt and Jack to get them ready. The beauty about (Greene) is if needed, he could step into that role just like that.”

This is important because USC is supposed to be a contender for the College Football Playoff and any loss could be critical.

Would a coach who waited until the fourth game to start Darnold insert the highly regarded Sears into an early game? Not only would he end Sears’ redshirt season, he would gamble Sears is ready to perform.

Greene might be the perfect choice but requires practice. So Fink seems to be in a nice situation, at least as the short-term backup.

It also be unfair to Sears to expect him to just come in and perform if needed. Darnold had a redshirt year, after all.

But true freshman no longer require a transition. Jake Browning (Washington) and Josh Rosen (UCLA) proved it two years ago. And if given the chance, Darnold would have been as good or better. It would have been too politically incorrect to play him over Cody Kessler in 2015, though.

“You see the talent there (with Sears),” Martin said. “He’s doing anything you want a young quarterback to do.”

But a redshirt is probably the best course. Unless USC needs a quarterback for a month or longer.

Bottom line: Darnold needs to stay healthy.