Lions coach Jim Caldwell said Walker was in surgery Tuesday afternoon but wouldn't say whether the surgery was taking place in Seattle, where the injury happened, or back in Michigan. Caldwell said the team would eventually place him on injured reserve.
"You certainly feel for him because he's one of those guys that just kept getting better and better every week and working at it," Caldwell said. "That's the tough part of this game."
The 6-foot-3 Walker signed a one-year deal with the Lions as a free agent in the offseason after spending his first three seasons with New Orleans. He beat out Caraun Reid and Gabe Wright for a starting job and had nine tackles in his first four games before the injury.
When asked about the extent of Ngata's injury Tuesday, Caldwell said to check the injury report that will come out Wednesday. After Monday night's loss to Seattle, Ngata said he wasn't too concerned about the injury but was likely scheduled for an MRI on Tuesday.
Caldwell also declined to give updates on tight ends Eric Ebron or Brandon Pettigrew. Ebron injured his knee in the first half against the Seahawks and did not return. A league source told ESPN Insider Adam Caplan that an MRI on Ebron's left knee showed no structural damage. When asked about this, Caldwell declined to comment on the report.
Caldwell also would not say whether the team planned on signing another defensive tackle this week.