The Washington Redskins fear they will lose linebacker Reuben Foster for the 2019 season with a torn left ACL suffered Monday on his first play in the team’s first offseason workout at Redskins Park.

Foster is scheduled to see a specialist, just to be sure the diagnosis is correct, but doctors were sure he had suffered a severe knee injury, according to a person with knowledge of the situation who wasn’t authorized to comment publicly.

Foster’s absence would be a significant blow to the Redskins, who had hoped the linebacker would develop into an impact player and leader for their defense.

“It’s very concerning, for sure,” Coach Jay Gruden said. “We will have to wait and see before I get too emotional about it.”

Foster fell to the ground during the first practice drill — a light team scrimmage — and appeared to be in considerable pain as he pounded his hand against the turf. Gruden, team president Bruce Allen and defensive coordinator Greg Manusky all looked on as Foster was tended to by the team’s training staff.

Foster remained on the ground for about 10 minutes before he was lifted onto a cart and taken off the field with an air cast on his left leg.

Gruden said Foster stepped on the foot of offensive lineman Tyler Catalina, landed “funny” and “felt something happen in his leg.”

One player said he heard Foster yell in pain. Someone shouted, “He’s down!” and as the group of players moved away, Foster remained in a heap on the grass. Several players stopped to look and seemed to offer words of encouragement, but as coaches called for everyone to move to the next drill, Foster alternated between lying flat on his back with hands on his helmet and rolling on his side, grabbing his leg.

The Redskins’ acquisition of Foster last fall was heavily scrutinized, given his two domestic violence arrests last year, the second of which led to the San Francisco 49ers releasing him Nov. 24. Washington claimed him two days later with the hope the charge would be dropped and he would be able to play this season. The charge was indeed dropped in January, and the NFL cleared Foster to practice just before the start of OTAs.

The Redskins believed that Foster would fill a huge hole at middle linebacker. He played well his rookie season in San Francisco, and Washington was certain it had gotten a talented defender at a bargain price. But Foster, who starred at Alabama with several of the Redskins’ other defensive players, had been injured in each of his first two years in the NFL, leading to questions about his durability.

He was suspended for the first two games last year, while a member of the San Francisco 49ers, following his first domestic violence arrest and a weapons charge in California, as well as an arrest for marijuana possession in Tuscaloosa, Ala. The domestic violence charges were later dropped, the weapons charge was reduced from a felony to misdemeanor and the marijuana charge was dropped when he entered a diversion program for first-time offenders.

Despite his on-field promise, Foster’s behavior seemed to frustrate San Francisco’s management enough that the team cut him immediately after the November arrest. San Francisco Coach Kyle Shanahan later said he was surprised another team had claimed him.

He bonded quickly with the Redskins, however, reconnecting with ex-Alabama teammates and building quick friendships with others on the team. Several people around the team have said he is popular in the locker room and well respected even by players who didn’t know him before.

Former Alabama teammate and fellow linebacker Shaun Dion Hamilton said that Foster had been “so anxious” to get back on the field with his new team, adding: “We had been talking about it since last year when we first got him. You just hate to see things like that to happen to a guy like Reuben, so jolly, always a happy person.”

Foster’s injury is a blow to a team that has been overrun with injuries in recent years, including quarterback Alex Smith’s possible career-ending broken leg in November and running back Derrius Guice’s torn ACL in the first quarter of the first preseason game. The Redskins finished 2018 with 24 players on injured reserve. They had 20 on IR in 2017.

“It’s the third [overall] play,” a stunned Gruden said after Monday’s practice. “It’s a jog-through tempo type play. . . . Three-quarter speed. . . . Got his knee tangled up.

“I don’t know how to process it, really. We’ve had some bad luck over here for the last couple years, but this one here takes the cake because this was a noncontact drill and there was really no contact involved in it. He just landed funny. But we have to move on. We have to get guys ready to play that are here. We’ve got to do the best we can to get Reuben healthy again and move on. . . . I wish I had the answer for you. Sometimes I wish we’d all just do walk-throughs and then go play on Sundays, but we’ve got to practice.”

Kareem Copeland contributed to this report.

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