And the depth at the position wasn't very commendable either. There's a reason why Mitch Unrein was more known for his touchdown catch last year than his skills at defensive tackle.
But now, the situation is completely different. Knighton emerged as a star last season, Sylvester Williams was added to the fold with a first-round draft pick and the Broncos' depth is looking fabulous.
Williams, who registered a sack in back-to-back games last year and showed promise at times, is entering his second year. Defensive tackles have a steeper learning curve than most other players, and Williams visibly had problems adjusting to the wear and tear of the NFL in his rookie campaign.
But now, the athletic monster is poised for a big season.
If he has one, he would be a fabulous complement to Knighton, who, according to Pro Football Focus (subscription required), ranked sixth among defensive tackles last season (including the playoffs) and was a menace in the postseason.
If, however, he doesn't meet his goals, the Broncos have other options.
Vickerson is a solid run defender who started and did a decent job last year. Unrein graded out positively on Pro Football Focus last year and has stuck around despite coming in as an undrafted free agent in 2011.
On passing downs, the underrated but talented Malik Jackson slides inside. He accumulated six sacks last year and earned very positive marks for his all-around play, and nothing less should be expected of him in 2014.
Jackson's presence fills a critical role on defense, allowing the run-stopping tackles to rest.
In addition, the Broncos added a wild card to the mix. Marvin Austin's signing with the Broncos wasn't big news, but it could end up being one of the team's most meaningful offseason acquisitions.
Austin was drafted in the second round in 2011. He could have been taken even higher without some off-field issues. However, injuries and those aforementioned issues have slowed his development, and he's never reached his peak.
In Denver, that could change.
Austin isn't going to start unless he noticeably outperforms Williams and others in training camp, but he'd still play if he makes the team. The Broncos rotate their defensive tackles frequently, giving everyone playing time and resting their starters.
Knighton didn't play much down the stretch in 2013, as, according to Pro Football Focus (subscription required) he saw action in fewer than 60 percent of Denver's defensive postseason snaps.
Williams played in fewer than 55 percent of those snaps despite starting. Malik Jackson does see a lot of time as a defensive tackle on pass-rushing downs, but there would still be playing time for Austin.
Vickerson, who went on injured reserve with a hip injury last November, will also be an option. He started over Williams before he got hurt, and he has a solid track record.
Unless he's a cap casualty due to his contract (two years, $4 million), he will stick around and see time.
However, there is a chance that Denver cuts ties with Vickerson. The cap space that the Broncos would get from this transaction could be rolled into the 2015 league year, and it could be used to sign impending free agents like Demaryius Thomas, Julius Thomas, Wes Welker, Rahim Moore and Chris Harris.
If that happens, Austin would have a firm grasp on a roster spot. Unrein could also be cut, as he is making a respectable $1.43 million.
Unrein, however, appears to have the inside track to a roster spot for another reason. He is the primary fullback that the team uses in goal-line situations, which is a relatively important role.
Denver rarely uses a fullback, but the position hasn't become extinct. Unrein has a very good chance to make the team once again, and his phenomenal work ethic and contributions to the team chemistry won't hurt.
After all, there's a reason why he's stuck around for three years despite going undrafted.
With Unrein likely to make the team and Williams and Knighton appearing to be locks, Vickerson and Austin will have to fight for the last spot. Because of Jackson and Derek Wolfe, who can both play defensive end or tackle without an issue, it's highly unlikely five defensive tackles will be carried.
In other words, relatively unknown roster hopefuls like Sione Fua will need a rash of injuries to make the team.
That also means that Vickerson and Austin will have to battle for the last spot. Given the lack of certainty about Austin and given the immense role Vickerson played in 2013, he's unlikely to be a cap casualty.
Still, the battle will be one to watch. Andrew Mason of denverbroncos.com has praised Austin's work so far, which isn't good news for Vickerson. The position is one to keep an eye on.
Expected starters Knighton and Williams will stabilize the position. Knighton has the ability to repeat his dominant 2013 campaign, and Williams is finally ready to show the talent the Broncos saw when they chose him in the first round in 2013.
As for the rest of the bunch, they can be counted on if the injury bug hits.
Jackson piled up six sacks and earned a plus-17.8 rating from Pro Football Focus, Unrein hasn't done much wrong in his time with the Broncos, Vickerson has always been a stout run defender, and Austin has always had the potential to be great.
In the end, the team will likely have to make a tough cut. However, the players the Broncos keep will likely keep offensive coordinators up at night.