Ahkello Witherspoon's season is over. An MRI revealed that the San Francisco 49ers cornerback sustained a sprained posterior cruciate ligament (PCL) during the first quarter of Sunday's 26-23 overtime victory over the Seattle Seahawks.

The injury isn't a major one and should not impact his availability for the 2019 season or the team's offseason activities, but with just two games left during this season, Witherspoon will not retake the field in 2018. He will land on injured reserve, head coach Kyle Shanahan told reporters on Monday.

Witherspoon landed awkwardly out of bounds while attempting to tackle Seahawks running back Chris Carson. He struggled early this season but rebounded nicely in recent weeks.

"I wish he could have finished these last two games," Shanahan said. "I think he definitely was finishing better than he started, but his story's not written yet. He's got to improve, and hopefully, he'll come back here ready to go next year, and take off the way he finished."

What is Shanahan's assessment of Witherspoon's performance in recent weeks?

"I thought he got a lot better in his coverage," Shanahan responded. "Just more consistent, playing a little more physical in his coverage too. I know he had some PI calls last month, ones that I wouldn't want him to play differently. I thought he did a real good job on all those, and I liked how he got more aggressive throughout the year."

Rookie Tarvarius Moore replaced Witherspoon at corner after Sunday's injury and will start during the 49ers' final two games, Shanahan confirmed. The team will host the Chicago Bears on Sunday before traveling to Los Angeles Memorial Coliseum for its finale against the Rams.

"I was excited to see him play," Shanahan said of Moore. "I know they challenged him a number of times. He missed some plays but I like how he rebounded throughout the game [...] Stuff that he struggled on earlier, I thought he did better in the fourth quarter.

"He plays physical. He doesn't mind hitting. He showed that on special teams. He carried it over to the defense. It looks like he had fun out there. It looked like it wasn't too big for him. He challenged guys at the line, and he made a huge block too on special teams on Richie's (James) kick return too, which sprung him loose."

The 49ers made Witherspoon a third-round draft pick out of Colorado in 2017. He has appeared in 26 games with 21 starts over his two seasons and registered 69 tackles, 11 passes defensed, two interceptions, and a forced fumble.