PITTSBURGH -- With the season-ending knee injury to Bud Dupree, the Pittsburgh Steelers will again turn to a once-unheralded player to replace a key contributor of their undefeated team.

Rookie Alex Highsmith is the latest in a series of replacements expected to keep the Steelers' 11-0 season rolling.

First, there was Chukwuma Okorafor replacing right tackle Zach Banner, whose season ended with an ACL tear in Week 1. Then it was Kevin Dotson filling in for veteran guard David DeCastro for almost three games. And, of course, beginning Week 6, former undrafted free agent and Western Michigan product Robert Spillane took over for inside linebacker Devin Bush, who tore his ACL against the Cleveland Browns.

"I'm just as comfortable as I was in Robert Spillane when we called upon him or Kevin Dotson when we called upon him on the other side of the ball," coach Mike Tomlin said of Highsmith stepping up in place of Dupree. "That's life in this business. Those guys work behind the scenes every day working very diligently preparing themselves for these opportunities not only in terms of knowing what to do, but just preparing themselves in terms of conditioning for when we ring their bell.

"We are ringing Alex Highsmith's bell now, so it will be exciting to watch him respond to it."

Though he's a third-round pick, Highsmith fits the Steelers' mold of the under-the-radar player suddenly given a big stage. A Charlotte product, the defensive end-turned-outside linebacker was hardly recruited out of high school. He began his college career as a walk-on in 2015 and eventually earned a scholarship during the summer of 2017.

He also only entered the NFL draft once he exhausted his college eligibility as a redshirt senior -- something Tomlin says he believes will help him in this situation.

"Oftentimes, we aren't drafting a lot of fifth-year seniors these days, so he had a maturity level beyond where he was at in this process," Tomlin said, recalling the 23-year-old Highsmith's pre-draft interviews. "But he's probably older than most rookies. I like his continual growth over the course of his career that manifests itself in the form of production. He had a really big year in 2019 at UNC-Charlotte.

"Those are some of the things that are attractive to us. He had a tangible, growing résumé and he had some maturity that we thought would aid us if called upon in the ways that he is being called upon right now."

Highsmith is charged with filling a major role in one of the NFL's best defenses. A pick made to draft and develop talent at outside linebacker, Highsmith has been a steady special-teams contributor, and he has played as many as 25 defensive snaps in a game. He also has one sack, one interception, 20 tackles and one quarterback hit.

The Steelers lead the league in sack rate (9.8%) this season, and they enter Monday's game against the Washington Football Team (5 p.m. ET, Fox) carrying a 68-game sack streak -- one off the 69-game record set by the Tampa Bay Buccaneers from 1999 to 2003. The Steelers also lead the league in scoring defense, sacks and takeaways -- something only two other teams have done this late in the season since the 1970 NFL-AFL merger, per Elias Sports Bureau research.

Dupree had eight sacks this season, second only to T.J. Watt's 11. Dupree also had 26 pressures, tied for second on the team and making him one of four Steelers with at least 20. No other team has that many players with 20 pressures, according to ESPN Stats & Information research.

A free agent last season, Dupree returned to Pittsburgh on a one-year franchise tag, a move made by the organization in large part to keep him and Watt together for at least another year. The pair has two of the three quickest get-off times in the NFL, per Next Gen Stats.

Tomlin, though, isn't worried about Dupree's absence impacting Watt's production.

"I don't think T.J. Watt gets assistance from anyone in terms of his quality of his play," Tomlin said. "T.J. makes his plays. I don't think that's going to be an issue at all. Guys like T.J. don't depend on anyone."

But like the other replacements, there's an intangible void that has to be filled with Dupree's absence. If Dupree wasn't the heart and soul of the defense, he was close to it. Wide receiver JuJu Smith-Schuster said the locker room after the win on Wednesday was quiet and dark as the team worried about Dupree. Roethlisberger referenced a "heaviness" that came over the team with Dupree's injury. Watt, a man of few words, posted a picture of the pair celebrating on Instagram afterward with the caption, "My Brother."

Known for his laser focus, Watt is known to be a lone wolf in practice -- with one exception.

"I don't know if he talks to anyone other than Bud [Dupree] in a practice setting," Tomlin said earlier this season.

Completely replicating that connection and chemistry will be impossible, but finding a way to replace it is necessary for the Steelers to move forward with their undefeated season. And the Steelers hope their search for a replacement begins and ends with Highsmith.