In television there's a term known as "jumping the shark" which is used to describe a show that is past its prime and in decline. All shows, from "Happy Days" to "LOST," reach this point no matter how good they once were at their apex. The same holds true for football players.

You could make the argument that Denver Broncos quarterback Peyton Manning has been the best passer in the NFL over the last 15 years. But you could also make the argument that Manning is now on his last legs, jumping the shark, if you will. Over the final five games of last season (including playoffs), Manning had a passer rating of just 79.9 and a completion percentage of just 62.3; far cries from his career averages of 97.5 and 66 percent. In that same span, the Broncos offense averaged 26.8 points. Before that: 30.1.

Denver fans have to wonder how much Manning is still capable of at this point.

"The Broncos quarterback will be headed to the Pro Football Hall of Fame the moment he is eligible," ESPN's Bill Williamson wrote. "But if Manning, who turned 39 in March, has a poor season, he will be second-guessed. Manning considered retirement after he sagged late last season following a hot start and an incredible 2013. He had one 300-yard passing game in his final seven games of the 2014 season, including the Broncos' one-and-done postseason. If Manning's fade continues early in this season, he will be questioned for coming back. With a new coaching staff and an unsettled offensive line, it won't be easy for Manning to stave off Father Time for another year. But he's Peyton Manning. He came back from multiple neck surgeries. He's up to the challenge."

Not helping matters will be the absence of Pro Bowl left tackle Ryan Clady, who suffered a torn ACL earlier this offseason and will be sidelined for the entire year. But as Williamson noted, Manning has proven doubters wrong before. His late season swoon last year is concerning, no doubt about that. But if there's anyone who's capable of going out in a blaze of glory, it's Peyton Manning.

Broncos fans will just have to cross their fingers and hope for the best.