PROVO — BYU's two-quarterback experiment came to an abrupt halt Tuesday with the news that junior Riley Nelson has been sidelined for the rest of the season with a shoulder injury — an injury that coach Bronco Mendenhall said was originally sustained during fall camp.

That opened the door for Jake Heaps to become only the second true freshman straight out of high school to start for the Cougars. His debut as a starter comes Saturday against Nevada (4 p.m., The mtn.).

"It's a great opportunity. It's unfortunate what's going on (with Nelson). But it's a time when I've got to step up and I've got to help this team the best that I can. That's what I'm going to try to do. The guys are rallying around me," the 19-year-old Heaps said after Tuesday's practice. "Being the quarterback at BYU is a special opportunity. It means a lot to me. I'm going to work as hard as I can and do everything I can to do this thing right."

He's said he's looked forward to becoming the starter at BYU for a long time.

"That's why I came here. I didn't come here to take half of it or not be the guy," Heaps said. "I came here to hopefully be the guy and when the time was right to lead the team, right now it happened. It was under unfortunate circumstances but it's an exciting opportunity for me."

After splitting practice reps, and playing time, with Nelson to this point, Heaps will now take almost all of the reps and snaps.

"It's been tremendous for my development and for my opportunity to grow," he said. "I feel myself getting better as each rep goes. We've got a lot of improvement to make. There's a greater opportunity for me to go out there and show what I'm capable of and give everything I have to this team and show everybody what kind of quarterback I can be."

With Heaps securing the starting role, sophomore James Lark now becomes the backup QB.

The coaching staff has been impressed with Heaps since he arrived on campus last winter. "I think he's very confident and he's looking forward to the chance and now it's an opportunity for him to get a ton of work," Mendenhall said. "We've always liked Jake's talent and the potential there. I liked two options and I was hoping to continue a complement of some sort along the way. Now there is one."

Asked if Heaps is prepared for this role, Mendenhall replied, "Who knows whether he's prepared or not? It's a freshman playing football. If there's anyone that is prepared, his experience to this point has led to me feeling very comfortable. I believe in his potential. It's just a matter of catching up on experience and playing football. He's very capable. It's just going to be decision-making, experience, execution, and just playing ball."

Mendenhall said Nelson hurt his non-throwing shoulder during fall camp, but that injury wasn't discussed publicly. Early in the Florida State game, the injury worsened after Nelson absorbed a hard hit.

Team trainer Kevin Morris described it as "a severe injury to the shoulder" and that Nelson will undergo surgery as soon as possible. "We felt like it was necessary right now to get it done," he said.

Mendenhall said Nelson couldn't raise his arm above his waist when the two talked Tuesday.

"He's given everything he's got. He tries so hard," the coach said. "There's no way just no way he could play anymore. ... It needs to be fixed right away. Looking at the MRI, that he made it this long is pretty impressive. Just because he's so dang tough."

After surgery, Nelson will undergo rehab for 5-6 months. Nelson told Mendenhall he plans to return to the program once he's healthy again.

"I think he wants to come back and I think he wants to play here and I think he wants to play quarterback," Mendenhall said. "That's what I'd like to see happen as well."

With Nelson out, BYU's team loses a lot, Mendenhall said. "We lose experience. We lose a lot of leadership. And we lose another option at quarterback. He's as disappointed as I am. And our team is."

Heaps played all but two series against Florida State, completing 15-of-31 passes for 114 yards and a touchdown pass.

The Cougars have scored only 47 points in three games and gained only 191 yards against the Seminoles. The previous week, BYU passed for just 88 yards against Air Force.

But Heaps is confident that the offense can put things together. "It's a matter of us going out there and executing," he said. "If we're executing on every play, we can put 50 points on the board every game."

Heaps emphasized that while he's excited to be the starter, he's focused on the team, not himself. "It's our team. It's not my team. There are 105 of us on this team. It's not just about me," he said. "I need to step up as a leader and I need to step up and make plays and demand a lot out of our guys. We're all excited for this week."

Cougars on the air

BYU vs. Nevada

Saturday, 4 p.m.LaVell Edwards Stadium, Provo

TV: The mtn.

Radio: 102.7 FM, 1160 AM