ENGLEWOOD, Colo. -- Peyton Manning has long offered parameters about what he must see in his play to add another season to his Hall of Fame résumé. The Denver Broncos quarterback said he must have the ability to protect himself from big hits, and, most importantly, help his team win.

"[Tom] Brady said he was going to play until he ... sucked," Manning said with a smile shortly before the season started when asked about the possibility of retirement. "That's a pretty good line. ... Some guys can hang on, can hang on and hang on and get another year vested, I guess, if that's the goal. If you can really produce and help a team, and you enjoy playing, I think that's up to the individual."

On Sunday night, a disappointing 24-13 loss to Indianapolis in the divisional playoff round ended Manning's 17th NFL season. In each of his three seasons with the Broncos, Denver has won the division title and at least 12 games. This season, Denver had the league's No. 2 offense, and Manning threw for 39 touchdowns, second in the league. But after the loss to the Colts, Manning offered no guarantees about 2015.

"I guess I just can't give that simple answer," said Manning, who played with a right thigh injury suffered in Week 15 against San Diego. "I'm processing it. I can't say that. I could not say that."

Clearly, Manning's play was not up to his standards in the second half of the season. The thigh injury, the continued struggles of the Broncos' offensive line, and opponents' strategy to shut down Denver's favorite passing routes contributed to the dip in his play.

Over the final eight regular-season games, Manning threw 15 touchdown passes and 10 interceptions. In Week 14 against Buffalo and Week 17 against Oakland, he did not throw a touchdown pass -- the first two games of his tenure in Denver in which he went without one.

The Broncos were 6-2 in the final eight games of the regular season, but the more Manning threw, the more difficulty the Broncos had winning. Denver was 2-5 this season when he attempted at least 40 passes. And, starting with the Nov. 2 loss in New England, the Broncos were 1-3 in games when Manning threw for at least 300 yards.

Most teams this season tried to work off Seattle's template from last February's Super Bowl. The Seahawks took away the Broncos' favorite pass routes -- the crossing routes and the screens -- and were physical with the Denver receivers. They consistently kept plays in front of them.

The thought was Manning, post-spinal fusion surgery, would not be able to accurately and consistently pass down the field on plays outside the numbers. Other teams tried to stop Manning similarly, but they had mixed results without the Seahawks' personnel or assignment discipline.

In Week 9, the Patriots, often leaving just a single safety deep, clogged the middle of the field. In the 22-point loss against New England, Manning threw for a season-high 438 yards, but he also threw two interceptions and could never take full advantage of the room he was given up the sidelines.

The following week, the Raiders didn't have the roster to hang with the Broncos, who won handily as Manning threw five touchdown passes. But Oakland batted down four passes early and intercepted Manning twice in the first quarter.

Then the Rams put it all together as they battered the Broncos' receivers, consistently got pressure on Manning and also intercepted him twice. St. Louis tried to force the ball outside, and the Broncos ran the ball just 10 times in the game. The result was a 22-7 loss, Denver's third of the season.

Buffalo Bills defensive coordinator Jim Schwartz, who almost universally played two deep safeties against Manning over the years, elected to play a single deep safety as well. The Broncos escaped with a 24-17 victory in Week 14. Schwartz had worked with Patriots coach Bill Belichick in Cleveland and had been a longtime assistant coach for Rams coach Jeff Fisher when Fisher was with the Titans.

Mix all that in with the fact the Broncos' offensive line couldn't consistently hold back the rush -- especially the middle of the field, where Manning needs space. His throwing motion is more lower-body dependent since his neck fusion surgery, and he needs room to stride to drive the ball down the field.

The Broncos made four changes in the offensive line during the season, and it was a big enough issue that they took an All-Pro right guard in Louis Vasquez and moved him to right tackle. Left tackle Ryan Clady made the Pro Bowl, but most personnel executives in the league believe Clady did not play close to his 2012 form. Clady surrendered a strip-sack of Manning on Sunday that resulted in a lost fumble.

Manning's targets also had issues. Tight end Julius Thomas hurt an ankle in November, receiver Demaryius Thomas had ankle and hand injuries down the stretch, and receiver Wes Welker was suspended for the first two games of the season and had more than four receptions in just three games.

Finally, there was the thigh problem, which was seemingly worse than Manning or the Broncos let on. The injury in Manning's plant leg further dialed back his ability to push the ball outside or deep with accuracy.

"I know he's been dinged up for a while,” said tight end Jacob Tamme, who was Manning's teammate with the Colts as well. "He's been grinding."

And that's where Manning arrives in the offseason. He needs to decide if his play late in the season was due to health or age. His decision whether to return depends on whether the Broncos repair their offensive front, and on Manning's ability to recover from his injuries. There's also no telling how Denver's coaching change will affect his plans.

"I hope he comes back," cornerback Chris Harris Jr said. "He's Peyton. He's done so much, I think he still has some football left in him."