ALAMEDA (AP) — The Oakland Raiders placed starting middle linebacker Nick Roach on season-ending injured reserve Wednesday after he was unable to recover from a concussion in the preseason.

Roach originally got hurt on Aug. 22 in the third exhibition game against Green Bay. He returned to practice on Sept. 3 on a limited basis but only took part in individual drills and he was never able to be cleared for contact. Now he is done for the season.

Roach was supposed to be the quarterback of the defense and his absence has played a big role in Oakland’s early struggles. After playing every defensive snap in his first year in Oakland in 2013, Roach has been unable to make it on the field this year.

The Raiders (0-4) have been plagued by miscommunication and alignment issues on defense without their signal caller. Oakland has the second-worst run defense in the NFL through four games with Miles Burris and Kaluka Maiava sharing the duty at middle linebacker.

Roach is Oakland’s second linebacker to be shut down for the season this week. Maiava was placed on injured reserve Tuesday with a hamstring injury.

The Raiders got some positive news at the position with outside linebacker Sio Moore back at practice Wednesday after missing the past two games with an ankle injury.

The Raiders signed Jamar Chaney on Wednesday to replace Roach on the roster. Chaney is in his fifth season in the NFL and was cut in training camp this summer by Denver.

He started 23 games from 2010-12 in Philadelphia, including all 16 in 2011, and played one game last season with Atlanta.

Chaney has 161 career tackles with one sack, three interceptions, 12 passes defensed and one forced fumble.

The Raiders had claimed linebacker Ray-Ray Armstrong off waivers from St. Louis on Tuesday. Armstrong joined St. Louis as an undrafted free agent out of Miami in 2013 and played all 16 games as a rookie. Armstrong has played four games this season and has been almost exclusively used on special teams.