By Chris Emma—

LAKE FOREST, Ill. (CBS) – Six days after dropping the ball, Jeremy Langford still held his regret.

Sitting in his locker stall at Halas Hall on Saturday, with his first career start at running back awaiting on Monday night, Langford, unsolicited, pointed to the added motivation. That third-down drop on the Bears’ attempt at a final drive last Sunday kept his team from a chance at the victory, instead setting up a Vikings victory.

“I’m more anxious than anything, just to make up for that play last game,” Langford said in looking ahead to Chicago’s contest in San Diego.

On Saturday, Bears coach John Fox officially ruled out running back Matt Forte against the Chargers. His knee injury is deemed too severe to play, and his status for the following Sunday in St. Louis looms largely in doubt. Enter Langford, the Bears’ fourth-round pick out of Michigan State.

NFL running backs can often be interchangeable, with an exception being Forte’s tremendous nine-year run in Chicago. Longevity for running backs is rare. All it takes is an injury or inconsistency and it’s “next man up.”

Langford has an important opportunity beginning Monday. He can emerge as the Bears’ next running back.

At season’s end, Bears general manager Ryan Pace must consider whether he will bring Forte back on a new contract. Set to turn 30 in December, Forte seems to have more good years ahead, though he’ll likely want a deal longer than Chicago will offer. Pace must have a plan for Forte’s replacement. Perhaps his fourth-round pick of the 2015 draft could be that option.

Late-round backs becoming NFL starters is a recent trend in the NFL. On Sunday, five running backs drafted in the sixth or seventh round were starters, and seven undrafted free agents were atop the depth chart. The league’s leading rusher was Devonta Freeman, a breakout star for the Falcons who was picked in the fourth round (103rd overall) in the 2014 draft. Langford went 106th overall a year later.

Like Freeman, Langford is a smaller, shiftier back with a versatile skill set. Bears teammates have touted Langford similar to Forte, believing in his abilities.

“He’s going to be a heck of a player for us,” quarterback Jay Cutler said of Langford.

From Kyle Long to Martellus Bennett and more, the Bears backed Langford’s abilities. They feel there’s little to no dropoff from Forte’s production.

Those weren’t just words of support, too – trust tackle Charles Leno on that.

“I practice with the guy – I believe it,” Leno said. “He’s a good back. I know he’s going to do his job and do it well.”

In seven games this season, Langford has 27 rushes for 80 yards, mostly coming in a reserve role behind Forte. He entered the 2015 campaign as the Bears’ third-string running back, but when Jacquizz Rodgers suffered a season-ending injury, Langford moved up. Now, it’s his time to shine.

Langford travels to San Diego with the trust of his offensive coordinator, Adam Gase, and his quarterback, Cutler. The Bears feel that they can use Langford much like they have Forte, making him a key piece of the passing game while relying on him to carry the rushing load. Behind Langford is Ka’Deem Carey and Antone Smith, each of whom is without a rushing attempt this season.

Without Forte in the backfield, Langford becomes the Bears’ workhorse in the backfield – for now and perhaps for years to come. He hopes to leave this chance with no regrets.

“You got to make the best of the opportunity,” Langford said, “and not let it slip through your hands.”

Follow Chris on Twitter @CEmma670.