OXNARD, Calif. -- Before the Dallas Cowboys even held their first padded practice of training camp, they suffered a blow to their defense with pass rusher Sam Williams suffering a torn ACL in his left knee, a source told ESPN on Sunday.

The injury ends Williams' season before it began.

Williams was injured during the special teams' portion of practice after he was engaged in a blocking drill. He remained down for several minutes as he was attended to by the Cowboys' medical staff. He could not put any weight on his left leg as he got on a cart and was taken to the locker room.

After practice, owner and general manager Jerry Jones said, "We didn't like what we saw," before Williams headed off for an MRI.

The Cowboys were banking on Williams being a major part of their pass rush behind DeMarcus Lawrence and Micah Parsons. In free agency, Dorance Armstrong and Dante Fowler Jr. joined former defensive coordinator Dan Quinn with the Washington Commanders.

They combined for 11.5 sacks last year.

Williams has 8.5 sacks in his first two seasons. He was third on the team in sacks with 4.5 in 2023, but he played just 28.3% of the snaps on defense. The Cowboys chose Williams in the second round in 2022 out of Ole Miss.

The Cowboys selected Marshawn Kneeland in the second round this year and have been impressed with his early work in training camp.

"Impressive. Very impressive. Very mature," coach Mike McCarthy said before Sunday's practice. "Love his physicality, motor, just like we did during the draft process. He's off to a good start. He's very comfortable, picks it up in the classroom. Outward personality, which is important. He's off to a good start."

The Cowboys have Viliami Fehoko Jr., Tyrus Wheat and Durrell Johnson as full-time defensive ends at camp but they did not record a sack last year. Chauncey Golston can play end and tackle and had 1.5 sacks last season.