SANTA CLARA, Calif. -- The San Francisco 49ers added two more players to their injured reserve list Saturday, one of which leaves them particularly thin at cornerback.
Nickelback K'Waun Williams is headed to injured reserve because of a sprained knee, which means he must miss at least the next three games. Defensive end Ezekiel Ansah (torn biceps) has also officially been added to injured reserve and will miss the rest of the season.
Williams joins starting cornerback Richard Sherman (calf) on IR and with Emmanuel Moseley out this week as he continues to deal with a concussion, the Niners will be without their top three cornerbacks for Sunday's game against the Miami Dolphins.
Backup cornerback Dontae Johnson has also been ruled out because of a groin injury and cornerback Ahkello Witherspoon is listed as questionable as he continues to deal with a hamstring injury.
All of that left the 49ers with no choice but to elevate a pair of cornerbacks from the practice squad for this week. Jamar Taylor, who will step into Williams' spot in the slot, has been promoted from the practice squad to fill one of the open roster spots created by placing Williams and Ansah on injured reserve.
In addition, the 49ers activated cornerback Brian Allen and receiver Kevin White from the practice squad in order to provide some temporary depth.
If Witherspoon is able to play Sunday, he is expected to start opposite Jason Verrett on the outside with Taylor in the slot. Ken Webster is the likely choice to start opposite Verrett if Witherspoon is ruled out before the game.
"That is probably our most fluid situation at DB," coach Kyle Shanahan said on Friday. "We'll see how some of these guys did after practice, how they're feeling based off the training room and we'll make our decisions and we'll go."
Sherman is still awaiting his chance to return from injured reserve after missing the past three games. He was eligible to resume practicing this week but he has yet to begin his 21-day window. Shanahan said they'd be a bit more cautious with Sherman and hope to have him back in time for the Week 6 game against the Los Angeles Rams.