With Peyton Manning one year older, a new coaching staff and a roster full of question marks, expect the Denver Broncos to regress in 2015.

The Denver Broncos had three years with Peyton Manning to win a Super Bowl. Their fourth year together won’t be so kind. Denver, despite seeing Manning return for his 17th season, has the look of a team on the decline without an easy way to slam the engine into reverse.

Manning, 39, is still one of the best quarterbacks in the National Football League. Yet, the days of him being able to single-handedly win a game are kaput. Over the last seven regular-season games and his playoff loss to the Indianapolis Colts, Manning completed 62.8 percent of his passes for 2,026 yards, along with 11 touchdowns and eight interceptions. He also struggled to be efficient with his throws, averaging a pedestrian 6.99 yards per attempt.

If you multiply those numbers for a full season, Manning remains a solid quarterback but only a remnant of the player he once was. Ultimately, Father Time beats all.

Furthermore, general manager John Elway had a curious offseason. With Manning perhaps playing in his last year, it would stand to reason the Broncos would go for broke before ushering in the Brock Osweiler era. Instead, Elway fired head coach John Fox and his staff, and replaced them with Gary Kubiak and his people, including defensive coordinator Wade Phillips. In nine years with a talented Houston Texans roster, Kubiak made the playoffs twice and never reached a conference championship game.

Most Broncos fans are thrilled for the change, but it remains an odd decision. Kubiak’s offense requires a mobile quarterback, something Manning will never be associated with. All of the misdirection and bootlegs Kubiak loves to utilize will be muted with Manning at the controls. On defense, Denver is switching from a 4-3 alignment to a 3-4. While the move will likely benefit edge-rushers Von Miller and DeMarcus Ware, it stands to cripple the defensive line. Regardless of whether you prefer Kubiak or Fox, the transition will take time to settle in.

Elway would have done well to retain nose tackle Terrance Knighton, but allowed him to leave for a very matchable one-year deal in Washington. With Knighton out of the picture, the Broncos are lining up Sylvester Williams, Derek Wolfe and Malik Jackson on the front. Frankly, it’s a group without much accomplishment. In a division with Jamaal Charles and Melvin Gordon, Denver could be exposed in the run game. With a bad run defense comes an impacted pass defense, with the linebackers having to cheat up.

Even with a strong secondary that features Chris Harris Jr., Aqib Talib and T.J. Ward, concerns remain. Talib is feast or famine, illustrated by his brutal performance in the AFC Divisional loss to the Colts. Ward is a terrific in-the-box safety, but middling in pass coverage. On Pro Football Focus, Ward ranked 34th of 87 graded safeties with a +1.9 grade. Yet, Ward was an ugly 81st in coverage, grading out at -7.2.

Offensively speaking, the Broncos took massive hits. Guard Orlando Franklin left via free agency for the San Diego Chargers, while left tackle Ryan Clady tore his ACL in Wednesday’s OTA session, putting him out for the campaign. Guard/center Manny Ramirez was dealt to the Detroit Lions, while center Will Montgomery signed with the Chicago Bears. From left to right, the offensive projects to be Chris Clark, Shelley Smith, Gino Gradkowski, Louis Vazquez and Ty Sambrailo.

With the aforementioned line, Manning might be throwing quickly out of self-preservation. Unfortunately for him, tight end Julius Thomas was allowed to leave for the Jacksonville Jaguars. Thomas is an overrated player, only catching 43 passes for 489 yards, ranking fourth and third on the team, respectively. The issue is replacing his first downs (30) and touchdowns (12), something Owen Daniels and Virgil Green are not likely to do. Thomas provided an athletic weapon underneath, and his absence allows defenses one less big-play threat to worry about.

The Broncos still have a pair of terrific receivers in Demaryius Thomas and Emmanuel Sanders. At running back, C.J. Anderson will be showcased in Kubiak’s run-heavy system. Denver will still score points, but a leaky offensive line and a black hole of production at slot receiver and tight end are hurtful. Unlike a few years ago, Manning needs help, and if his receivers are covered reasonably well, he won’t have a ton of it. For all of Anderson’s potential, he still needs blocks.

In totality, Denver has regressed while others in the AFC West have improved. The Kansas City Chiefs are the biggest threat to dethrone the Broncos for a multitude of reasons. Head coach Andy Reid is entering his third season with the team, and is seeing the return of defensive stars Derrick Johnson and Mike DeVito, after both tore their Achilles’ in Week 1 last year. Kansas City also signed receiver Jeremy Maclin and safety Tyvon Branch while acquiring guard Ben Grubbs from the New Orleans Saints for a fifth-round pick.

The Chargers are also improved and could return to the postseason in 2015. San Diego brought in Franklin from Denver, along with retaining Brandon Flowers in the secondary. Promising second-year corner Jason Verrett is back from shoulder surgery, and the offense remains strong with Philip Rivers, Antonio Gates and Malcom Floyd. The main question with the Chargers is their defensive front seven, something that is lacking badly outside of end Corey Liuget.

After winning four consecutive AFC West titles, the Broncos are teetering on the edge of oblivion. The roster is weakened on both sides, the coaching staff is completely remade and the star quarterback is aging rapidly. Clady’s injury only put into focus how many issues are facing a team normally penciled in for a playoff BYE week.

Denver will be relevant in December, but the holes in its roster will eventually catch up.