By Simon Evans

DALLAS (Reuters) - They are barely noticed, having played just one game between them this season, but the backup quarterbacks for the Green Bay Packers and Pittsburgh Steelers know that Sunday they could suddenly find themselves thrust into the Super Bowl spotlight.

The likelihood is that both Matt Flynn of the Packers and Byron Leftwich of the Steelers will watch the entire Super Bowl from the sidelines, but each knows they are an injury away from having the ball in their hands along with the responsibility for their team's fortunes.

If either needs a reminder that injuries do happen in key games, they only have to look back two weeks ago when Chicago Bears quarterback Jay Cutler left the NFC Championship game and backup Caleb Hanie took over.

"You definitely hope it doesn't happen, especially with a quarterback of the caliber of Aaron Rodgers, but you always have to prepare yourself as though it could happen," Flynn told Reuters Wednesday.

"You have to prepare mentally as if you are the starter. If you don't do that, it's not fair to your team mates and not fair to the guys you spend every day with."

Flynn has made one start in three years as Rodgers's backup -- last December against the New England Patriots -- and says he has had to learn how to deal with the frustration of working hard all week but not seeing any playing time.

"I was a backup for a few years in college, so I kind of learned mentally how to prepare yourself, to work and study all week and not get the gratification of the playing time on Sundays," said Flynn.

During practice, the backup operates as an opponent for the team's defense by simulating the upcoming opposition's quarterback.

Then comes the work in the 'quarterbacks room' where coaching staff and the team's three quarterbacks analyze video and discuss tactics.

That work behind the scenes is invaluable to the collective effort, according to Steelers quarterbacks coach Randy Fichtner.

"There is a recipe to getting the chance of Super Bowls and I see it every day in that room," he told Reuters. "What I respect is that they understand the role and as a coach you want everyone to know their role. There is no selfishness in the group and you can't ask for more than that."

While Flynn is hoping to emulate Rodgers, who was Brett Favre's understudy for three years before getting his chance, the 31-year-old Leftwich had starting roles with Jacksonville, Atlanta and Tampa Bay as well as in a previous stint with the Steelers when he won a Super Bowl ring from the bench.

Tall and with a commanding physique, Leftwich is as close to a carbon copy of burly starter Ben Roethlisberger.

"It's always frustrating when you don't get the opportunity to play in the game but winning is our priority. I've won games in this league, Ben's the starter but it is not like I have to prove anything to anyone about myself," Leftwich told Reuters.

(Reporting by Simon Evans in Dallas; Editing by Frank Pingue; To query or comment on this story email sportsfeedback@thomsonreuters.com)