Washington Redskins linebacker Reuben Foster was carted off the field Monday with a season-ending torn left ACL, according to multiple reports.
The Redskins sent Foster for an MRI exam after the injury, coach Jay Gruden told reporters after the first workout of the team's offseason program.
"Reuben, the type of player that he is, the type of energy that he brings, he wouldn't be laying down unless something was wrong. We'll hope for the best right now until we get the results, but very concerning for sure," Gruden said after the workout.
"I'll just have to wait and see before I get too emotional about it."
Foster was emotionally distraught as he was assisted to the cart and into the locker room with an air cast on his left knee.
Foster crumpled to the ground on the third play and immediately was tended to by defensive coordinator Greg Manusky and team president Bruce Allen. Allen was observing the workout from nearby.
Gruden said Foster, in a non-contact drill while going about three-quarters speed, stepped on guard Tyler Catalina's foot and "landed funny on his left leg."
"Very disappointing what happened," Gruden said. "His first rep as a Redskin, he runs through the gap and gets injured. ... He's devastated. He's obviously guarded right now. He felt something happen in his leg. But he's very upset about it.
"I don't know how to process it really. We've had some bad luck over here for the past couple of years, but this one here takes the cake."
NFL linebacker Reuben Foster
NFL linebacker Reuben Foster
TUSCALOOSA, AL - APRIL 19: Reuben Foster #10 of the Crimson team looks into the backfield of the White team during the University of Alabama A-Day spring game at Bryant-Denny Stadium on April 19, 2014 in Tuscaloosa, Alabama. (Photo by Stacy Revere/Getty Images)
Jan 7, 2017; Tampa, FL, USA; Alabama Crimson Tide linebacker Reuben Foster (10) during the Alabama Crimson Tide media day at Amalie Arena. Mandatory Credit: John David Mercer-USA TODAY Sports
ATLANTA, GA - DECEMBER 31: Alabama Crimson Tide linebacker Reuben Foster (10) walks onto the field prior to the Chick-Fil-A Peach Bowl football game between the Alabama Crimson Tide and Washington Huskies on December 31, 2016, at Georgia Dome in Atlanta, GA. Alabama won the game 24-7. (Photo by Todd Kirkland/Icon Sportswire via Getty Images)
TAMPA, FL - JANUARY 09: Quarterback Deshaun Watson #4 of the Clemson Tigers is tackled short of the first down by linebacker Reuben Foster #10 and defensive back Minkah Fitzpatrick #29 of the Alabama Crimson Tide during the third quarter of the 2017 College Football Playoff National Championship Game as defensive back Marlon Humphrey #26 of the Alabama Crimson Tide looks on at Raymond James Stadium on January 9, 2017 in Tampa, Florida. (Photo by Brian Blanco/Getty Images)
KANSAS CITY, MO - AUGUST 11: San Francisco 49ers linebacker Reuben Foster (56) flexes after his teammates made a defensive stop in the third quarter of an NFL week 1 preseason game between the San Francisco 49ers and the Kansas City Chiefs on August 11th, 2017 at Arrowhead Stadium in Kansas City, MO. The 49ers won 27-17. (Photo by Scott Winters/Icon Sportswire via Getty Images)
Aug 27, 2017; Minneapolis, MN, USA; San Francisco 49ers linebacker Reuben Foster (56) looks on following the game against the Minnesota Vikings at U.S. Bank Stadium. Mandatory Credit: Brace Hemmelgarn-USA TODAY Sports
Sep 10, 2017; Santa Clara, CA, USA; San Francisco 49ers linebacker Reuben Foster (56) is loaded onto the injury cart during the first quarter against the Carolina Panthers at Levi's Stadium. Mandatory Credit: Kelley L Cox-USA TODAY Sports
SANTA CLARA, CA - SEPTEMBER 10: Christian McCaffrey #22 of the Carolina Panthers talks to Reuben Foster #56 of the San Francisco 49ers after their game at Levi's Stadium on September 10, 2017 in Santa Clara, California. (Photo by Ezra Shaw/Getty Images)
GLENDALE, AZ - OCTOBER 01: San Francisco 49ers linebacker Reuben Foster (56) walks the sidelines prior to an NFL game between the Arizona Cardinals and San Francisco 49ers at the University of Phoenix Stadium on October 1, 2017 in Glendale, Arizona. (Photo by Robin Alam/Icon Sportswire via Getty Images via Getty Images)
SANTA CLARA, CA - NOVEMBER 05: San Francisco 49ers outside linebacker Reuben Foster (56) celebrates after making a tackle during an NFL game between the Arizona Cardinals and the San Francisco 49ers on November 5, 2017 at Levi's Stadium in Santa Clara, CA. (Photo by Robin Alam/Icon Sportswire via Getty Images)
SANTA CLARA, CA - NOVEMBER 05: Arizona Cardinals running back Adrian Peterson (23) and San Francisco 49ers outside linebacker Reuben Foster (56) pose for a picture after exchanging their jersey's with each other during an NFL game between the Arizona Cardinals and the San Francisco 49ers on November 5, 2017 at Levi's Stadium in Santa Clara, CA. (Photo by Robin Alam/Icon Sportswire via Getty Images)
CHICAGO, IL - DECEMBER 03: Daniel Brown #85 of the Chicago Bears carries the football against Reuben Foster #56 of the San Francisco 49ers in the fourth quarter at Soldier Field on December 3, 2017 in Chicago, Illinois. The San Francisco 49ers defeated the Chicago Bears 15-14. (Photo by Joe Robbins/Getty Images)
HOUSTON, TX - DECEMBER 10: Reuben Foster #56 of the San Francisco 49ers talks with Official Allen Baynes on the field prior to the game against the Houston Texans at NRG Stadium on December 10, 2017 in Houston, Texas. The 49ers defeated the Texans 26-16. (Photo by Michael Zagaris/San Francisco 49ers/Getty Images)
SANTA CLARA, CA - DECEMBER 17: San Francisco 49ers outside linebacker Reuben Foster (56) brings down Tennessee Titans running back Derrick Henry (22) during the game between the Tennessee Titans verses the San Francisco 49ers on Sunday, December 17, 2017 at Levi's Stadium in Santa Clara, CA (Photo by Douglas Stringer/Icon Sportswire via Getty Images)
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The Redskins claimed Foster off of waivers when the San Francisco 49ers parted with the troubled linebacker last season. The 49ers let Foster go in the wake of a domestic violence accusation stemming from an alleged incident during a team road trip to Tampa, Fla.
Foster, 25, was a first-round pick out of Alabama in 2017 (31st overall). He has played in 16 of a possible 32 games in his career.