With less than one month before free agency begins, the Denver Broncos have a lot of work to do.

Especially on their defensive line.

Derek Wolfe, Shelby Harris, Adam Gotsis and Joel Heath are all unrestricted free agents while 2019 surprise Mike Purcell is a restricted free agent. Simply, the likelihood of Denver re-signing all of them is incredibly small.

Harris has emerged as a star and signed Drew Rosenhaus; he’ll be banking in big time this offseason. Derek Wolfe enjoyed one of his best-ever seasons, but he’s on the wrong side of 30 and will also be expensive. Mike Purcell should, without a doubt, be re-signed and his restricted status means the Broncos can match any offers sent his way.

But, that will leave them with holes (multiple) to fill.

Pro Football Focus, who recently wrote on the 50 biggest free agents, says the Broncos will sign two of those top 50; Justin Simmons and defensive lineman Michael Pierce.

Simmons is a no-brainer; he’s a homegrown talent, a great locker room presence and the best safety in the NFL last year per Pro Football Focus.

Pierce is more the surprise, and the analytics website predicts Denver will even sign him to a relatively cheap 3-year, $15 million contract.

Pierce is a 6′ 340-pound beast of a defensive lineman, and PFF says he would fill the role that Harris leaves; they may be partially right. From an interior defensive lineman perspective, Pierce gets after the quarterback well. Last season — his worst of his four in the NFL per PFF — Pierce totaled 12 hurries, three QB hits and one sack. And he’s averaged 13 pressures per season, with five total sacks over the course of his career.

But, to be fair, PFF missed a few things. First and foremost, Harris is the NFL-leader in batted balls over the last two seasons with 13. When he’s not rushing the passer — 13 sacks in three years — Harris knows exactly when to get his hand up and disrupt a pass at the line of scrimmage. Conversely, Pierce has only one batted ball in his four-year career.

The other thing PFF missed is this: They say because of Pierce’s down season, the Broncos will get him at a $5 million per year deal. But, they also say Harris will sign a similar, 3-year $5.5 million per year contract with the Detroit Lions.

Look, if Harris is willing to sign for a mere $0.5 million more per season, the Broncos will just retain his superb services. But, the bad news is Spotrac says Harris’ “market value” is a whopping $12.3 million per season.

He’ll likely sign for around $10 million a year, which is why the Broncos won’t be able to retain him.

But, Pierce does seem like a mostly capable replacement, and he’s younger than Harris by a year. Signing Piece and then re-signing Purcell sets the Broncos up with a solid interior defensive line, at least at that tackle position, moving forward. Then, they’ll need to turn their eyes toward defensive ends.