The Washington Redskins saw a once-encouraging contingency plan at quarterback fall apart a bit when interim starter Kirk Cousins left the team’s 24-13 preseason victory over the visiting Pittsburgh Steelers on Monday night with what is being described as a “mid-foot sprain.”

The timeline for Cousins’s recovery wasn’t immediately known, but for the time being, Washington is down to just one healthy, experienced quarterback — 11th-year veteran Rex Grossman — as Robert Griffin III’s quest for a Week 1 return remains uncertain.

Cousins left FedEx Field on crutches and in a walking boot. X-ray results came back negative, but the quarterback still will have an MRI exam Tuesday morning to provide a clearer indication of the extent of the injury.

“They feel like it’s mild right now, so that’s a good sign,” Redskins Coach Mike Shanahan said before later adding, “He’ll get an MRI tomorrow. But at least it was a good sign with the doctors today.”

Meanwhile, orthopedist and team consultant James Andrews observed Griffin for the first time since late July and met with team officials to discuss the quarterback’s recovery. But he wasn’t expected to make a decision on whether Griffin should open the season as Washington’s starter or wait longer before returning.

The injury to Cousins overshadowed a victorious effort at FedEx Field by the Redskins, who improved to 2-0 on the preseason.

Despite the uncertainty hovering over Griffin and his reconstructed right knee, the Redskins have expressed confidence throughout the offseason about the stability of their quarterback position because of Cousins’s presence on the roster.

As a rookie, the Michigan State product performed well in place of Griffin, and Cousins took the bulk of the first-team snaps in the offseason to ensure his readiness if Griffin suffered a setback in his recovery.

Cousins reinforced the Redskins’ confidence in him with a strong showing in the preseason opener just over a week ago and looked to build on that against the Steelers.

But the opposite happened. Cousins and the offense put up pedestrian numbers in two first-quarter series. The quarterback completed 2 of 3 pass attempts for 19 yards and was sacked once, and the offense went 0 for 2 on third down on his drives.

Shanahan’s original plan called for Cousins to play roughly one half, but Cousins lasted just more than a quarter before he was injured on a running play.

On first and 10 from his own 20, Cousins scrambled up the middle for a seven-yard gain. On the next play, Cousins rolled out. Finding no one open, he scrambled again, gaining another seven yards before getting knocked out bounds by Steelers linebacker Lawrence Timmons. Cousins grabbed his right foot, stood up and limped to the huddle, but he sat down shortly after and pointed to his right foot as trainers rushed out to him.

“I felt it initially, and as I was walking back to the huddle, I started to self-evaluate about could I change directions if needed and be an athlete, and I started feeling it and decided, ‘You know what? Preseason game No. 2 with a long season ahead of us, now is not the time to try to be a hero,’ ” Cousins said.

Rex Grossman took over and played the remainder of the second quarter and all of the third quarter, completing 10 of 16 passes for 133 yards, a touchdown and an interception. Pat White played in the fourth quarter and completed 3 of 6 passes for 22 yards and an interception.

Cousins wasn’t the only key player who suffered an injury for Washington. Nose tackle Barry Cofield left with a fracture in his right hand, but he and Shanahan said they didn’t expect that to keep him sidelined. Wide receivers Leonard Hankerson and Aldrick Robinson suffered right knee and left thigh injuries, respectively. But neither injury is believed to be serious.

Injuries aside, the Redskins enjoyed some early game positives, which were supplied mainly by the starting defense.

The unit demonstrated again an ability to both get to the quarterback and generate turnovers. Despite playing without leading pass rusher Brian Orakpo, who missed the game while nursing a bruised right thigh, the Redskins flustered Ben Roethlisberger, sacking him once, hurrying him two more times and forcing him into an interception that was returned for a touchdown.

The Redskins held the Steelers to three-and-out on the opening possession of the game, and on the next, Cofield and defensive end Kedric Golston combined for a sack on Roethlisberger.

On second and 16 from the Pittsburgh 28, linebacker Ryan Kerrigan got his hands up and blocked Roethlisberger’s pass at the line, juggled the ball for six yards, then secured it as he rumbled 22 yards for a touchdown.

“Hopefully I didn’t waste a pick-six in the preseason, but it felt good to get in the end zone,” said Kerrigan, who has returned an interception for a touchdown in each of his first two NFL seasons. “We didn’t force any turnovers in the first game, so to get a couple of them out there, it felt good. Hopefully more to come both this week against Buffalo and then in the regular season.

In the next quarter, Kerrigan registered a sack-fumble on backup quarterback Bruce Gradkowski, and Cofield recovered. Washington running back Keiland Williams fumbled one play later, giving the ball back to Pittsburgh.

But the Redskins’ defense registered another turnover — this time on a play by rookie safety Bacarri Rambo.

Rambo entered the game looking to redeem himself from an open-field whiff that led to a 58-yard touchdown run by Chris Johnson in Tennessee the week before. But the sixth-round pick missed on two open-field tackle attempts in the early going Monday.

However, Rambo made up for it. He darted into the backfield, tackled Pittsburgh running back Jonathan Dwyer behind the line of scrimmage and knocked the ball free with his left hand.

Washington linebacker London Fletcher recovered the fumble, and two plays later, the Redskins scored on a 10-yard touchdown pass from Grossman to Hankerson, who leaped into the air, snagged the high pass with his left hand, pulled it down and tucked it into his belly for the catch.

Grossman directed a late-second quarter drive for a 38-yard field goal that led to a 17-6 lead at halftime. The Steelers pulled within 17-13 on a 10-yard Derek Moye touchdown catch from Landry Jones. But Roy Helu Jr. gave his team breathing room again, scoring on a 30-yard run up the middle with 3:21 left in the game.

The Redskins now have a quick turnaround before they host Buffalo on Saturday. Tuesday represents a rest and treatment day, and the team will practice Wednesday and Thursday and have a walk-through Friday. At this time, it remains unclear whether Cousins will play, but if not, Grossman said he is ready to handle a heavier workload.

“I don’t think anything changes for anybody,” he said. “You just go out there and try to make the most of your opportunities. Bottom line, I think Kirk is going to be healthy by Saturday, and when I get in, I’m going to ball. I don’t try to overthink it. Just go in, ball out, let the chips fall where they may.”