ENGLEWOOD, Colo. -- It was 370 days ago when the Denver Broncos closed out the 2019 season swirling with optimism after a win over the Raiders on a sunny 31-degree day in downtown Denver.

On Sunday, the Broncos close out the 2020 season against the Raiders (4:25 p.m. ET, CBS) -- Las Vegas this time, not Oakland -- and any optimism for the future now stands side-by-side with the disappointments of this season.

As coach Vic Fangio put it this week when asked to rank the season's losses: "They're all equally tough, every one eats at you in different ways, for different reasons. But a loss is a loss and they suck."

The Broncos are 5-10, already guaranteed their fourth consecutive losing season and fifth consecutive season of missing the playoffs. No matter what happens inside Empower Field at Mile High Sunday, the bottom line will say they took a step back from last year when they finished 7-9 with wins in four of their final five games behind their then-rookie quarterback Drew Lock.

That drive through last December set the stage for what the Broncos hoped would be significant improvement in 2020. Hope that was derailed early and often.

The Broncos will close the football year with 13 players on injured reserve, including starters such as Von Miller, Jurrell Casey, Courtland Sutton, Bryce Callahan and Phillip Lindsay. They had their share of battles with COVID-19, including defensive coordinator Ed Donatell's hospital stay that caused him to miss six games, as well as a game played without quarterbacks when Drew Lock, Brett Rypien and Blake Bortles sat out due to violations of COVID-19 protocols after Jeff Driskel had tested positive for the virus.

On the field, they struggled in other ways. Fangio has often talked about the need to make "winning plays." To that end, it is Lock who likely carries the biggest to-do list into the offseason. He enters Sunday's game last in the league in completion percentage and tied for last in interceptions.

At his best there was the four-touchdown effort against the Carolina Panthers or the second-half efforts against the Chargers. But there was the missed start for violating the COVID-19 protocols and inconsistent footwork that often led to the turnovers that will lose him the job if they continue at the current rate in 2021.

"Moving forward, I think the mistakes we're making -- I'll just take it all the way back to that -- the mistakes we're making have taken points off the board," said offensive coordinator Pat Shurmur.

"He's going to get it, it's going to click for him, and we need it to click for him," Broncos running back Melvin Gordon said of Lock. "I feel like we have a window with this team and he is the piece that's going to make or break us."

The Broncos project to be in the middle of the NFL pack in terms of salary-cap room this offseason -- enough to participate aggressively for a high-end player or two if they wish. They have major decisions to make regarding the team options on the contracts of Miller and safety Kareem Jackson.

They still have an offense that scored 16 or fewer points seven times this season, including the no-quarterback game, after failing to score more than 16 points nine times in 2019. They haven't had Miller and Bradley Chubb together in the defense since 2018, didn't force enough turnovers (last in turnover margin at minus-20 with the next worst at minus-10) and special teams -- again -- has had more difficult moments than spectacular ones.

"If we all get on the same page this offseason, I think our team can be very dangerous," said left tackle Garett Bolles. "... When you look on paper, we're neck-and-neck with some of the best teams in the NFL when it comes to talent. Plus, the little things that we have to really focus on and dial in -- not turning the ball over, converting third downs and keeping the chains moving."

After a season without a real offseason, Fangio has said he was told he will return in 2021. Lock is expected to at least get a we-like-what-we-see-but-a-lot-of-work-needs-to-be-done vote of confidence next week when John Elway speaks publicly about the plans to come.

Three quality draft classes have the Broncos with a youthful, potentially-impactful roster just waiting for a fourth consecutive one to help nudge them back into a postseason conversation.

"We had an inordinate amount of injuries, which I think hurt our progress some ... we turned it over too much, which hurt our progress," Fangio said. "We didn't get takeaways, which hurt our progress. I think individually, there's been a lot of progress. We've gotten a lot of young players a lot of playing time that they're going to grow from and learn from, and I think that's where the progress has nearly been made."