He was Carolina's defensive coordinator from 2011 to 2016 and directed the defense that helped the Panthers go 15-1 in 2015 and play in Super Bowl 50.
McDermott's defenses were 5-7 when going up against quarterback Matt Ryan and the Atlanta Falcons.
For some reason, McDermott elected to cover Falcons two-time All-Pro wide receiver Julio Jones with a single player last season. Jones ravaged the man-to-man coverage, catching 12 passes for a team-record 300 yards and a touchdown in the 48-33 plastering of the Panthers on Oct. 2.
Because of the Panthers' overall body of work on defense and clearly not that game, McDermott was hired to lead the Bills, who will face the Falcons at 1 p.m. Sunday at Mercedes-Benz Stadium.
The Bills have some solid corners in rookie Tre'Davious White and E.J. Gaines, but he's not likely to leave them alone with Jones, who'll be limited in practice this week with a back injury, but is slated to play.
Safety Micah Hyde, a former Green Bay Packer, will likely be nearby or free safety Jordan Poyer.
Ryan sees some of the traits of the Panthers in Buffalo's defense.
"They are aggressive," said Ryan, the league's reigning most valuable player. "Very aggressive front four. The linebackers are very good against the run. That's something that we've seen from Carolina. They have some of the best in the league.
"I think that carryover is the same. In the secondary, there's a lot of quarters type of coverage, which they do a great job with. They have a ton of different pressures. They give you a lot of different looks."
The Bills have 10 sacks this season.
"They put a lot of stress on your pass protections," Ryan said. "It's something that we'll have to do a great job of. I think communication on our end, making sure that everybody is on the same page is going to be really important this week."
McDermott and Falcons head coach Dan Quinn's paths have crossed before.
"I've known Sean McDermott for years," Quinn said. "He was a player at William & Mary when I was coaching there."
Quinn followed McDermott's career as he served as a graduate assistant at William & Mary (1998) before he went to Philadelphia (1999-2010) and then Carolina before landing the Buffalo job.
However, the Bills do have a strong front seven. Right defensive end Lorenzo Alexander, left defensive end Shaq Lawson and strong-side linebacker Jerry Hughes all have two sacks each. Also, tackle Kyle Williams is stout.
Marcell Dareus missed the Denver game with an ankle injury.
"He's always had a hard-nosed approach," Quinn said of McDermont. "They'll be really good tacklers and they've got a talented front."
Defensively, the Falcons will face their stiffest test of the season in the run game. Chicago's second-year back Jordan Howard was coming off a strong year, but the Falcons haven't seen a back as accomplished as LeSean McCoy yet.
McCoy has rushed 48 times for 140 yards and has caught 18 passes for 131 yards.
McCoy, fullback Mike Tolbert and quarterback Tyrod Taylor lead a rushing attack that averages 111.3 yards rushing per game (11th in the league). They also have former Falcons fullback Patrick DiMarco, who's being used as a lead blocker. He played 15 of 65 offensive snaps (23 percent) in their 26-16 win over Denver on Sunday.
The Falcons are giving up 85 rushing yards per game, which ranks ninth in the league. The Falcons held the Lions to 71 rushing yards.
"The way they're built, you can count on their run game being rock solid, and that starts with Shady, it goes through Mike Tolbert, and Patrick DiMarco is the lead blocker there," Quinn said. "They've got a good offensive line, and their quarterback can really run and is athletic."
Tyrod Taylor has rushed 24 times for 106 yards.
"I guess this will be about three weeks in a row that we see a guy that can extend plays and get outside the pocket," Quinn said. "Three weeks ago, we saw it with Green Bay, last week with Detroit, and now this week with Buffalo."
Taylor has been efficient in Buffalo's short passing game. He's completed 53 of 79 passes (67.1 percent) for 562 yards, four touchdowns and just one interception. He has a passer rating of 99.2.
"We know when the quarterback can extend plays, a second play just begins, receivers now have routes to go to different spots," Quinn said.
SERIES HISTORY: 12th regular-season meeting. Falcons lead series, 7-4. The Falcons have won the last four games with the last being a 34-31 victory in Toronto in 2013.
The Falcons are off to a 3-0 start for the second time under head coach Dan Quinn. The Falcons started off 5-0 in 2014, his first season with the team. But then things went downhill as they finished 8-8.
So, they are not ready to throw a parade after jumping out to a 3-0 start again.
"We'll go right back to the process every week to treat it the same," Quinn said. "For us, we feel like we're just getting rolling. It's just three games into it, and there is a lot of work to be done."
The Falcons needed goal-line stands against Chicago and Detroit to post wins on the road. The 10-second rule helped them escape against the Lions.
"It was definitely one of the most unusual endings to a game that I've been a part of, and as you went back through it, you just appreciate the strain of it," Quinn said.
The Falcons beat the Lions while losing the turnover battle, 3-0.
"To get in the plus, you have to create some takeaways," Quinn said. "We felt like we missed a few opportunities there."
Starting right tackle Ryan Schraeder is in the concussion protocol. The Falcons are hopeful he'll be able to return for the Buffalo game.
"First of all, I am optimistic that we'll get him back this week," Quinn said. "I am optimistic that we'll get him back this week ... He's still in the protocol as we're going through it."
The Falcons acquired Ty Sambrailo from Denver for a fifth-round pick on Sept. 1. He's played right tackle for Schraeder and while he gave up two sacks against the Lions, he was solid.
"I liked that there was urgency in the way that he would cut (block)," Quinn said. "I thought that he improved from the performance before."
He didn't anchor well on the two sacks he gave up.
"I think the issues that came up on the sacks are things that we can clean up on," Quinn said. "Where we can get our hands tighter and get a better punch. But I thought in the run game, I really felt his presence."
NOTES: WR Taylor Gabriel had his first touchdown catch of the season against the Lions. The 40-yard touchdown catch was Gabriel's sixth career touchdown of 30 yards or more and his seventh touchdown reception of 25 yards or more. ... WR Julio Jones was hit in the back on the team's last offensive play against Detroit. When he went to the sideline, he wouldn't immediately let the doctors check on him. Later in the locker room, he said that he could have returned to the game. Jones was limited in practice, but is expected to play against the Bills. ... DT Jack Crawford has a shoulder injury and was limited in practice. ... DE Vic Beasley Jr., who's recovering from a hamstring strain/tear injury, was slated to start running with the trainers off to the side at practice. He was injured in the victory over the Green Bay Packers on Sept. 17 and did not play against the Detroit Lions on Sunday. ... RB Terron Ward (neck/shoulder) was slated to return to running. He did not play against Detroit. ... FS Ricardo Allen is in the concussion protocol and did not practice. ... RT Ryan Schraeder remains in the NFL's concussion protocol and did not practice. ... DT Courtney Upshaw (ankle) did not practice and is not likely to return from injury for Sunday's game against the Bills.