Broncos quarterback Brock Osweiler scrambles as the Cardinals’ Justin Bethel lines him up during their exhibition finale on Thursday at Sports
Broncos quarterback Brock Osweiler scrambles as the Cardinals' Justin Bethel lines him up during their exhibition finale on Thursday at Sports Authority Field at Mile High. (Joe Amon, The Denver Post)

There is a future quarterback plan at the Broncos' Dove Valley headquarters, although John Elway would never dare draw it on paper. Wouldn't want any visible evidence for Peyton Manning to see.

But if the laws of mortality hold, the day will come when Manning, now 37, no longer is the Broncos' starting quarterback. If it can happen in Indianapolis, it can happen here.

That day might be four years away. It might arrive after next season. It might be for a quarter and a half while Manning ices a twisted ankle during this soon-to-be-starting season.

The future quarterback's name is Brock Osweiler.

In the Broncos' 32-24 loss to the Arizona Cardinals in the fourth and final preseason game Thursday night at Sports Authority Field at Mile High, Os- weiler played as though he's ready, should coach John Fox call on him for the present.

Osweiler's first three drives did not need to be cut up and spliced into a highlight reel. No edits needed.

On his first drive, which ended in a touchdown, Osweiler drilled intermediate completions to Gerell Robinson and Jake O'Connell.

On his second drive, which resulted in a short Matt Prater field goal, Osweiler gorgeously floated a 45-yard, post-pattern completion to Robinson.

On his third drive, Osweiler demonstrated mobility, running once for 11 yards, another time for 10.

He started with 7-of-7 passing, finished the first half 7-of-11 for 108 yards and was rewarded by getting the second half off. It was easily Osweiler's most polished and productive effort since Elway, the Broncos' boss of football operations, selected him out of Arizona State in the second round of the 2012 draft.

"Obviously as a football player, a quarterback, a competitor, I always want to play," Osweiler said. "It's hard to sit back and watch someone else play. At least that someone else is probably a first-ballot Hall of Famer. That makes it a little bit easier.

"I got better this preseason. And now, shoot, it's Peyton's turn to go out there and lead us."

Elway also has a backup plan to the future: Zac Dysert. Selected in the seventh round this year, Dysert started the second half and on his first possession threw a 25-yard TD pass to Robinson.

Osweiler, who stands a shade under 6-foot-7½, was drafted five weeks after the Broncos signed the free-agent Manning to a five-year contract. Manning The Man. Osweiler The Future.

Year 1 was all Manning. He nearly won his fifth league MVP award by leading the Broncos to a 13-3 record with the second-best statistical season of his 14-year career. Osweiler attempted a couple of mop-up passes.

Manning appears better in Year 15. He is healthier and more familiar with the Broncos' system and receivers.

There are enormous expectations on the Broncos as they get ready to kick off the NFL season next Thursday against the team that ended their 2012 season, the Baltimore Ravens. And Manning is the primary reason the Broncos are the prohibitive favorites to win the Super Bowl. He won 11 games in a row last year. He adds Wes Welker this year.

Osweiler is not close to Manning's level. There are no plans at Dove Valley, not even those tucked inside the noggins of the Broncos' brain trust, that conceive such a notion. But the idea this preseason was to push Osweiler's development so that if called upon to temporarily lead the offense, the Broncos could still find a way to win. In his four preseason games, Osweiler was 38-of-58 passing, an impressive .655 completion percentage. He didn't fumble or throw an interception in his one half of play against the Cardinals.

Osweiler's preseason is done. Will he play again this season? Not if all goes well for Denver. But he looks ready, just in case.

Arizona Cardinals running back Ryan Williams spins free as tight end Kory Sperry, a former Colorado State star, blocks Broncos defensive back Ross Rasner
Arizona Cardinals running back Ryan Williams spins free as tight end Kory Sperry, a former Colorado State star, blocks Broncos defensive back Ross Rasner during the first half Thursday night at Sports Authority Field at Mile High. The Broncos hosted the Cardinals in the final game of the preseason. (John Leyba, The Denver Post)

"This year I'm way more comfortable with the total package," Osweiler said. "I understand our protections, I understand what we're trying to do in the run game, I understand our checks.

"Without question I'm way more comfortable this year. And if my number gets called, hopefully I can step in and the team won't skip a beat."

Mike Klis: klis@denverpost.com or twitter.com/mikeklis


Key moment — When the final seconds clicked off the clock and it was confirmed that nobody had run into the visor-wearing Peyton Manning on the sideline and injured him.

Key stat — 133 yards. Brock Osweiler's total offense in his one half of work. He was 7-of-11 passing for 108 yards, without a touchdown or an interception, and ran for 25 yards on four carries.

Did you notice? — Von Miller didn't play a down. In explaining why he used Miller with the starters against the Rams last Saturday, coach John Fox said he didn't want to stretch Miller's suspension from six to eight games. So it's fair to say the Broncos settled on seven. Terry Frei, The Denver Post