"It is very unfortunate," Rivera said of Forrest. "He's a heck of a young man. He's had a good start to his career. He has played a lot of football already and this is his third season, but it's very unfortunate because you saw the growth and development.
"That's a big blow for us," Rivera later added on Reaves. "Obviously we have some guys on practice squad that we're going to look at and we will be elevating. A couple of those guys are guys that are special teams guys as well."
Forrest (shoulder) and Reaves (knee) were both placed on Injured Reserve on Tuesday after the Washington Commanders' 40-20 loss to the Chicago Bears. Technically, both are eligible to return after four weeks, but with no timetable for their return, it's not clear when either will be back on the field.
Enter Quan Martin and Percy Butler, who Rivera said would be elevated to fill the open roles. Both players, while talented, are still in the developmental stages of their careers, but with the team leaning more heavily on them going forward, the increase in snaps will be a chance to show what they can do.
"We drafted Percy for a reason," Rivera said. "We got Quan for a reason, and this is why. So now it's the next man up mentality, and we just gotta go forward and get ready."
The Washington continued preparing for their Week 6 matchup against the Atlanta Falcons. Take an inside look at how practice went on Thursday.
For Butler, it will be a moment for him to build on what was an impressive preseason and training camp for the former fourth-round pick. Butler believed he had a taken a step forward with his development in Year 2, and he backed up those claims with multiple pass breakups in practice and an interception against the Cleveland Browns.
So far, Butler has not been able to completely replicate that performance during the regular season. He has eight tackles in the last five games with two pass breakups, one of which could have easily been an interception against the Arizona Cardinals.
Butler is hopeful that more snaps will lead to more opportunities to make plays.
"I'm still not where I want to be, but I feel like I'm getting better every game," Butler said. "I'm learning new things, learning from every mistake and not making the same mistake constantly."
For Martin, Sunday's game could be the first time the rookie gets a defensive snap. All of his playing time has been on special teams so far. Martin had more of an up-and-down training camp. In practice, he got reps with the starting defense and flashed at points in the team drills; during preseason games, he was more inconsistent, although he did grab an impressive interception against the Baltimore Ravens.
Despite the lack of snaps on defense, Martin has tried to stay prepared for whenever his name is called.
"When that opportunity presents itself, just knowing that I'm prepared and knowing that I'm ready," Martin said.
Defensive coordinator Jack Del Rio kept things to the point when asked about what he expects from Martin and Butler: "Step up.
"Really unfortunate injuries. DFo's a great member of this squad and Reavo as well, we'll miss those guys. When those things happen and they do in this game, it's next man up and they get an opportunity to show what they're capable of and the team's counting on them."
Butler and Martin will face a unique challenge when they step on the field against the Atlanta Falcons. Their offense is in the bottom half of the league in yards per game, but they also have the potential for explosive plays, which has been a problem for the Commanders' defense, with Drake London, Kyle Pitts and Bijan Robinson.
Against players of that caliber, Butler knows that he and the rest of the defense needs to be focused on the details.
"Make sure everybody is being urgent," he said. "Everybody swarm to the ball. Just simple things that we could do would make us better. I feel like that's all we lack."