SANTA CLARA – Ahkello Witherspoon had a difficult afternoon Sunday against the Detroit Lions at Levi's Stadium.

Lions quarterback Matthew Stafford virtually ignored Richard Sherman’s side of the field and focused on Witherspoon. When targeting the 49ers' second-year cornerback, Stafford completed eight of the 12 passes for 99 yards and two touchdowns, according to Pro Football Focus. Stafford missed some open receivers down the field. Witherspoon was also called for two penalties and missed a tackle.

But Witherspoon was playing on a bum ankle, and 49ers coach Kyle Shanahan took the blame for even putting Witherspoon in that situation.

“He wasn’t 100 percent, and he wanted to play, but after watching the tape and everything, I don’t think I should’ve had him (play),” Shanahan said on "49ers Game Plan," which airs on NBC Bay Area (Ch. 3) on Saturday at 7 p.m.

“I shouldn’t have played him last week because we didn’t get his best and he obviously wasn’t ready to do that, so I’m going to make sure that I don’t put him out there unless he is 100 percent. I think we’ll find that out (Sunday) before the game.”

The 49ers may not know with Witherspoon and strong safety Jaquiski Tartt (shoulder) until Sunday morning if they will be able to play against the Kansas City Chiefs at Arrowhead Stadium.

Kansas City’s Patrick Mahomes threw 10 touchdown passes in the team’s first two games – the most by any NFL quarterback through two games. On the day before his 22nd birthday, he became the youngest player to pass for six touchdowns in a game in the Chiefs'  42-37 victory over the Pittsburgh Steelers.

 

Shanahan said the Steelers’ defense made it too easy on Mahomes and his speedy wide receivers, Tyreek Hill and Sammy Watkins, with too many blown coverages. The 49ers’ secondary must be a lot more disciplined, regardless of who lines up at cornerback and safety.

“You watch that Pittsburgh game, and there’s about six plays in the first 2 ½ quarters where guys were wide open in busted coverages,” Shanahan said. “If you give this quarterback and that speed a bunch of freebies by making mistakes, that’s the results will be.

“We’ve got to make them work for everything. And the way you do that is you stay sound, you don’t make mistakes, you got to be willing to give up some check downs, but don’t give up the touchdown. We have to be smart, disciplined, stay on top, and when they check it down, we need 11 guys swarming to the ball.”