Daniels, a starter, was hurt on the initial play of 7-on-7 offense vs. defense drills. He stayed down on the turf for several minutes before being taken away on a cart, a towel draped over his head. He's expected to have surgery Friday.
The Redskins also lost another defensive end, reserve Alex Buzbee, to a season-ending injury during their afternoon practice. Buzbee ruptured his Achilles' tendon.
Day 1 of Jim Zorn's training camp debut as an NFL head coach also included this sight: Cornerback Fred Smoot threw off his left shoe and clearly was in pain after wideout Santana Moss landed on him during the afternoon practice. It turned out Smoot sprained his ankle and is expected to only miss a week or less.
"I love sprained ankles now, because we know that's just a few days' deal," Zorn said, cracking a smile.
He was more serious while speaking about the loss of Daniels, who has played 12 seasons in the NFL with Washington, Chicago and Seattle. His 59 career sacks rank 17th among active players.
"The hard part is he was so ready, and he did everything that he could possibly do to not just have a great training camp but an excellent football season," Zorn said. "And now he's got a new challenge before him, and of course we have a new challenge before us."
Demetric Evans will move into Daniels' starting spot. Evans has played six NFL seasons, with 12 starts and 9½ sacks in 80 games.
"You always want to take advantage of opportunities," said Evans, who added that Daniels "has been a big brother."
The Redskins began training camp with Erasmus James sidelined. He's a former first-round pick who has had serious knee injuries, and Zorn said he doesn't expect James to be able to begin practicing until next month.
Cerrato said defensive lineman J.T. Mapu, who was released last month, was being flown into town and would be at practice Monday.