While the Detroit Lions’ defense has been plagued by injuries all season, their offense has remained largely healthy—until now.

Head coach Dan Campbell announced Monday that running back David Montgomery sustained a knee injury during Sunday’s loss to Buffalo, which will require surgery and sideline him for the season.

“He’s the ultimate teammate,” Campbell said of Montgomery, who played through the injury on Sunday. “Ultimate competitor.

We’ll miss him. He’s one of those guys who helped get us to this point. We owe him that much.”

Montgomery’s absence leaves Detroit without one half of its elite running back duo.

This season, Montgomery has rushed for 775 yards with a 4.2-yard average per carry and 12 touchdowns, tying him for fourth in the league with Green Bay’s Josh Jacobs and Los Angeles Rams’ Kyren Williams.

He’s also contributed 36 receptions for 341 yards.

The Lions will now rely heavily on Jahmyr Gibbs to lead the NFL’s fourth-ranked rushing offense.

Gibbs has been exceptional, with 1,047 rushing yards this season and 11 touchdowns. His 5.6 yards per carry trail only Lamar Jackson (6.4), Saquon Barkley (5.9), and Derrick Henry (5.8).

Gibbs has also caught 39 passes for 395 yards and three touchdowns.

“We have a lot of trust in Gibbs,” Campbell said. “He’s continued to improve throughout the season.

When given the chance, he’s made big plays. He showed that again on Sunday.

He adds an explosive dimension, and his work in the pass game keeps improving. We have a lot of confidence (in him).”

Campbell added that Craig Reynolds and rookie Sione Vaki will see expanded roles as Gibbs’ backups.

Reynolds has a career average of 4.3 yards per carry.

Detroit will undoubtedly miss Montgomery’s tough, inside running style, but the offense isn’t expected to shift much with Gibbs stepping up.

Gibbs is the only player in franchise history to record 70-plus scrimmage yards in each of the first 14 games of a season.

He also tallied his eighth 100-yard scrimmage game this year, finishing with 114 yards and two touchdowns against Buffalo.

This isn’t Gibbs’ first time taking over for Montgomery. Last season, Montgomery missed three games—Week 3 vs. Atlanta, Week 7 in Baltimore, and Week 8 vs. Las Vegas.

Gibbs shined in a win over the Raiders, carrying the ball 26 times for 153 yards (5.8) and a touchdown, while adding five receptions for 37 yards.

In those three games, Gibbs totaled 54 carries for 300 yards (5.5) and two touchdowns, along with 15 catches for 97 yards.

With two more key defensive injuries on Sunday—defensive lineman Alim McNeill (ACL) and cornerback Carlton Davis III (jaw)—the Lions’ offense will need to step up, and that puts more responsibility on Gibbs to excel as the primary running back for the remainder of the season.