Washington coach Ron Rivera confirmed the news Monday during his weekly video conference call.
Rivera did not specify the exact nature of the injury, referring to it as a leg injury. But sources told ESPN on Sunday that team officials feared Young had suffered a torn ACL.
Young will undergo surgery to repair the knee. It's a tough ending to a somewhat tough season for Young, who had just 1.5 sacks one season after winning Defensive Rookie of the Year.
"It's definitely sad," Washington defensive tackle Jonathan Allen said. "It's going to be tough, but knowing Chase's personality, knowing the way he works and the kind of guy he is, he'll come back stronger than ever."
Young suffered the injury with 7 minutes, 49 seconds left in the second quarter when he rushed quarterback Tom Brady on a third-and-2. Young went to the ground without much contact and writhed in pain.
When the cart came onto the field, Young waved it off and opted to limp more than 30 yards to the tunnel, with the help of teammate Brandon Scherff for part of the walk and then with athletic trainers.
Washington was already down one starting defensive end, as Montez Sweat suffered a broken jaw on Oct. 31 at Denver. He will miss another three to five weeks. Casey Toohill and James Smith-Williams will start at the end positions with rookie Shaka Toney as a primary backup. Smith-Williams and Toohill are both in their second seasons. All three are seventh-round picks replacing first-rounders.
"They're big, athletic and can move," Rivera said of Young and Sweat. "Those guys are hard to find."
Rivera said they liked how Young had been playing the run and were excited to watch him this week after what they considered strong practices, especially as a pass-rusher.
"He had some good moments early in the game. It was promising," Rivera said. "You do lose the threat of that type of player coming off the edge now. We have a couple workman guys who get an opportunity. We'll see how they handle it."
He said Washington also might end up blitzing more to generate edge pressure. It also can create interior pressure with Allen and fellow tackles Daron Payne and Matt Ioannidis. Allen leads Washington with six sacks.
Young, the No. 2 pick in the 2020 draft, was also a captain and had become an energetic leader for Washington.
"It's hard to see a guy like that go down for us," Washington receiver Terry McLaurin said. "He's a dominant player for us. He's a leader for us."
Last season, Young earned Defensive Rookie of the Year honors as he recorded 7.5 sacks. In the second half of last season, he recorded four sacks, forced three fumbles and recovered three. He set up other pass-rushers with his pressure. This season, coaches wanted him to improve his rushes, from eliminating stutter steps to just sticking to his area. But they also saw Young develop into a vocal presence.
"That's one of the things you want, a guy who not only says something but at some point will make an impact play," Rivera said. "That's the tough part you have to replace. ... Somebody will have to step up."