No amount of film study has prepared Peyton Manning for this. He enters the NFL postseason uncertain about his football future. After 18 years as a pro and at the age of 39, his body is breaking down and his skills are slipping. Passes he once made with ease now wobble and sail off target.

He is still one of the best quarterbacks in the league, but he now wins games more with his brain and his experience than with his arm. And he knows it.

So is this it? Almost two decades after completing a storied college career at the University of Tennessee, is it time for Manning to walk away?

I think so. The spirit is willing but the blunt force trauma of too many savage hits over too many NFL seasons has taken a toll. Time waits for no quarterback, not even Peyton Manning.

He recently told reporters in Denver that he has contemplated his future. “I’d be lying if I said I’m not thinking about that,” he said. But he plans to stick with his customary process of waiting until March to make the call.

That’s been his approach in recent years. It allows him to get a little distance from the previous season, taking some of the emotion out of the decision.

Just the same, I’m betting Manning will know what next year holds when he walks off the field for the final time in the postseason, whether that is the AFC semifinal or the Super Bowl.

This isn’t about Xs and Os, about reading your keys and sensing that a safety blitz is coming. This is a decision you make with your gut.

In many ways, it is a similar situation to the one Manning faced in January 1997. He had just quarterbacked the Vols to a 10-2 season and a No. 9 national ranking. The deadline for underclassmen to declare for the NFL draft was approaching, and he had to decide if he would skip his senior season or not.

In typical Manning fashion, he got out a pad and a pen and listed the pros and cons of going pro. Ultimately, he went with his gut and returned for one more season of college ball.

But he was 20 years old back then and secure with the knowledge the NFL would still be there in a year. Injuries were not a factor. His best football was ahead of him. That’s no longer the case. In recent months, Manning has been forced to confront his football mortality.

Peyton Manning is fighting age, injury and the accusation that he used human growth hormone in 2011 while recovering from neck surgery. The former Vol holds the NFL record for passing yards with 71,940.

-- Eric Bakke Via Ap

If this is the end, it’s been a remarkable career, capped by a season of change and challenges. The Broncos hired a new head coach, Gary Kubiak, who rewrote the offensive playbook. Manning suffered a foot injury and ultimately got benched. He was blindsided by allegations he had used human growth hormone (HGH) in 2011.

“You learn about yourself and how you handle it,” he said recently. “That’s been my theme all year: Just keep being a pro. I’ve been through a lot of stuff.”

That’s an understatement.

Last month, Al Jazeera reported that Guyer Institute, an anti-aging clinic in Indianapolis, supplied Manning with HGH four years ago. At the time, Manning was recovering from neck surgery. HGH is considered a performance enhancing drug and is on a list of banned substances for NFL players.

According to the report, Manning obtained HGH through packages sent to his wife, Ashley Manning. The key informant in the Al Jazeera report is Charlie Sly, a former unpaid intern at Guyer Institute. Sly has since recanted his accusations against Manning.

Manning has vehemently denied the report.

Peyton Manning admires the Vince Lombardi Trophy after the Colts’ 29-17 win over the Chicago Bears in 2007’s Super Bowl XLI, his only Super Bowl championship.

-- Ap Photo/Amy Sancetta

Still, the report puts NFL headquarters in an awkward position. Commissioner Roger Goodell spent months and hundreds of thousands of dollars in pursuit of another high-profile quarterback, Tom Brady, in the Deflategate matter. Should Manning get the same kind of scrutiny?

It’s a tough call. There are no indications Manning ever failed a drug test. And since almost five years have passed since the report alleges he took HGH, it would be difficult to find corroborating evidence.

Some have wondered why Manning doesn’t sue Al Jazeera for defamation if he is indeed innocent. Baseball stars Ryan Howard and Ryan Zimmerman, whose names surfaced in the same Al Jazeera report, have both filed suits, each claiming one count of libel and one count of invasion of privacy.

But that’s a tricky one for Manning.

A lawsuit would require him and others, including his wife, to give sworn testimony in depositions. That isn’t something Manning wants to do, based on past experience.

In May 2002, former University of Tennessee trainer Jamie Ann Naughright sued Manning, his father Archie and ghost writer John Underwood for statements attributed to Manning in the book, “Manning: A Father, His Sons, and a Football Legacy.’’

In the book, Manning characterized Naughright as having “a vulgar mouth.”

In March 2003, Manning spent two days giving a deposition, answering questions that ranged from his interaction with a coach in high school to an alleged “mooning” incident involving Naughright when Manning was a junior at UT.

That lawsuit ultimately was settled out of court for an undisclosed amount. But the experience of being grilled by a prosecution attorney in a two-day deposition probably makes Manning reluctant to file a defamation lawsuit.

For someone who appears so open and accessible in commercials and endorsement appearances, he is notoriously private when it comes to his personal life. Likewise, he always has shielded his wife from public scrutiny.

It remains to be seen what, if anything, the league office will do about the report. No doubt, Manning hopes the HGH story goes away and the NFL chooses not to pursue it.

Yes, it’s been a challenging season on the field and off. Statistically, it is Manning’s worst as a pro. His passer rating (67.9) is the lowest among starting quarterbacks. He’s thrown almost twice as many interceptions (17) as touchdown passes (9).

But it is a foolish person who writes off Manning, as recent developments showed.

On Jan. 3, Denver entered the regular-season finale against San Diego without a secure spot in the playoffs. The Broncos also entered that game without Manning in the huddle.

He had not played a snap since the 6:34 mark of the third quarter on Nov. 15. That’s the day he heard boos from Broncos fans when he threw his fourth interception of the day.

With Denver trailing the Chargers 13-7, Manning replaced Brock Osweiler midway through the third quarter. The Broncos rallied for a 27-20 victory. It was the 54th time in his pro career that Manning has directed the game-winning drive in the fourth quarter or overtime. That’s the most by any quarterback in NFL history.

That victory made Denver the No. 1 seed in the AFC, assuring the Broncos of home-field advantage as long as they advancing to the Super Bowl.

Thus, Manning’s story is still being written. If this is indeed an encore, it is worthy of a standing ovation.

David Climer covered Peyton Manning for four years at the University of Tennessee and in several NFL games, including the victory in Super Bowl XLI. Reach him on Twitter @DavidClimer.