The Washington Football Team could be without its starting quarterback, Alex Smith, and its top running back, Antonio Gibson, on Sunday when it hosts the Seattle Seahawks in a significant conference matchup.

Smith, the 36-year-old veteran who has guided Washington to a four-game winning streak and the top spot in the NFC East, is dealing with a right calf strain that limited him in the early going of the team’s win over the San Francisco 49ers this past weekend and ultimately sidelined him for the second half.

Smith did not practice Wednesday, but both he and Coach Ron Rivera declined to make any predictions about his availability for Sunday against Seattle (9-4), saying that the injury and his progress will be monitored throughout the week.

“I feel all right. Just taking it day by day,” Smith said. “I know you guys don’t want to hear that. Obviously we keep making improvements. It’s early in the week here, and we’ll see as it goes on.”

Smith described the strain as “a freak thing” but acknowledged it was an issue before the 49ers game.

“It was something that [was] very minor last week,” he said. “I practiced and felt good on it all week. For me, it was there a little bit but certainly not inhibiting me at all. And then in the game it quickly got worse, to the point where it was really, really affecting me and my ability dropping back and being able to decelerate and push off. I felt like it was affecting me a ton, especially those last several drives [of the first half], really kind of battling with that mentally, with how much it was affecting me and limiting me out there.”

Smith said the injury is “not at all” related to the more significant one he suffered to the same leg in 2018, when he had a compound fracture and blood infection that required 17 surgeries to resolve.

The anatomy of his leg, however, is different as a result of the surgeries. Much of the muscle tissue around his right shin was removed and replaced by muscle from his left leg. That new muscle is for filler and blood supply to the repaired bones. He doesn’t have nerve function, which is why he has foot drop and has to wear a brace to help him overcome it. His calf is original to his right leg and has its nerves intact.

The decision on Smith could be made late in the week, although Rivera warned he could take it all the way to game day. Because of Smith’s experience, he may not need to practice before suiting up Sunday.

“A smart football player like that, you usually don’t worry about those guys,” Rivera said. “Those guys are able to pick it up and be ready to go.”

Should Smith be unable to play, second-year quarterback Dwayne Haskins would start with a backup who is yet to be determined. The team has two quarterbacks on the practice squad: undrafted rookie Steven Montez and recent signee Taylor Heinicke, who played for Rivera and offensive coordinator Scott Turner with Carolina in 2018.

Haskins took all of the individual reps at quarterback Wednesday during the team’s walk-through practice, which was held inside because of snow. Haskins played the second half against the 49ers and, much like he did early in the season when he was the starter, showed flashes of potential and signs of needing development.

Heinicke is the team’s “quarantine quarterback” but in a loose sense. He remains distanced from the other three in the locker room and meetings but still practices with the full team.

Washington could be without Gibson for a second game because of the turf toe he suffered early in its Week 13 win at Pittsburgh. Although Rivera said Gibson has made “good progress” in his recovery, the running back did not participate in practice Wednesday.

Against the 49ers, Peyton Barber and J.D. McKissic carried the load and combined for 105 rushing yards. But Barber was on the injury report as well Wednesday with an ankle injury that limited him in practice.

It doesn’t appear that Gibson will go on injured reserve. But for depth and experience, Washington will sign veteran running back Lamar Miller off Chicago’s practice squad, pending a physical and negative coronavirus tests, according to people with knowledge of the situation. Miller will not be available for Sunday’s game because of the six-day pre-entry protocols, but if he passes, he would be available for the team’s final two regular season games, at home against Carolina and in Philadelphia, as well potential playoff games.

A 2012 fourth-round pick by the Miami Dolphins, Miller, 29, suffered an ACL injury during preseason last year with the Houston Texans and has since played only five offensive snaps. He spent training camp with the New England Patriots but was released as initial rosters were formed and later signed to the Bears’ practice squad.

Washington did not protect one of its practice squad running backs for Sunday, but if Gibson is unable to play, Javon Leake will probably be elevated again for depth.

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