LONDON -- With quarterback Alex Smith ruled out because of a separated shoulder, San Francisco 49ers head coach Mike Singletary is gambling on Troy Smith being able to turn his struggling team around.

Singletary said Wednesday the former Heisman Trophy winner will get his first NFL start in three years after Alex Smith was ruled out for 2 to 3 weeks with a separated left shoulder. The Niners play the Denver Broncos at London's Wembley Stadium on Sunday.

Singletary picked the former Ohio State standout ahead of David Carr, who came on against Carolina after Alex Smith was injured on Sunday but threw a costly late interception that led to the winning field goal for the Panthers.

"Troy Smith gives us a good opportunity to win this game," Singletary said. "I talked to David Carr about it. He understands. We had a couple of conversations about it. That's a personal thing between he and I, and I'm going to leave it there. Troy Smith is our starting quarterback."

With the Niners off to a 1-6 start, Singletary has little to lose by taking a gamble.

Troy Smith spent the last three years with Baltimore, where his only two starts came in the 2007 season as he struggled to live up to the hype from his college days. But the mobile quarterback, who could give San Francisco's offense extra options with his scrambling ability, said he wasn't surprised by Singletary's decision.

"The way that you prepare as a professional athlete, you have to be prepared when your number is called. And that's exactly where I'm at," he said.

The Niners have a bye following the game at Wembley, giving Alex Smith a chance to heal before San Francisco faces the St. Louis Rams on Nov. 14. He was tackled from the blind side by Carolina's Charles Johnson, driving his shoulder into the turf. He arrived in London on Monday -- along with the rest of the team -- and spent the morning at the hospital, still with his non-throwing arm in a sling.

Singletary said Troy Smith had never taken first-team snaps in practice with the Niners before this week, but that he's catching on quickly.

"He's been studying since we got here, and has been getting with the coaches as much as he possibly could," Singletary said. "He has enough of the offense to play."

Troy Smith said he was told "a couple of days ago" that he would start and would "continue to prepare like a madman" for the rest of the week.

"I think the easiest way to get through to your teammates that you're serious about what's going on is to know exactly what your job is, know exactly what everyone expects from you and go out and execute," Troy Smith said. "At the same time you have to respect your boundaries. I believe in not stepping on anybody's toes, I believe in getting in where you fit in."

While the quarterback will be leading a new team in completely new surroundings -- in front of about 85,000 British fans -- there is one reason he might feel right at home.

Troy Smith will be linking up once again with wide receiver Ted Ginn, one of his best friends from childhood and a favorite target throughout his playing career.

The duo played together both in high school in Cleveland and at Ohio State, and Ginn said they can't wait to get out on the field again together.

"It's great to be able to get back in tune with a guy that you've been playing with your whole life," Ginn said. "For us to go out and continue our journey that we've been [on] so far is great."

Ginn, who joined the Niners from Miami this season, said he first met Troy Smith when they were 7 years old and their families went to the same church. Back then though, their conversations didn't focus on football, but on who was going to sneak out to get some snacks.

"It was at church, and we had a McDonalds to our left, and we had a little candy store to our right," Ginn said. "And we would sneak out of the church, and either I would hold the door and he would run to McDonalds, or he would hold the door and I would run to the candy store. That's how we started off, and then we just grew from there."

Troy Smith said he isn't about to favor his old buddy if other targets are open.

"It's not just about my brother Ted Ginn, it's about the other receivers that are going to be out there also," he said. "We have tremendous playmakers everywhere, and it's my job, my duty, to get everybody the ball."