ALAMEDA, Calif. -- The chances are growing that the struggling Oakland Raiders' defense could have the daunting task of playing against Tom Brady and the New England Patriots on Sunday without starting linebackers Sio Moore and Nick Roach.

Moore has an ankle injury he suffered against Houston and Roach has been out with a concussion suffered against Green Bay on Aug. 22. Moore hasn’t practiced this week and Roach has been limited, but not cleared, for full contact, and coach Dennis Allen didn’t sound overly optimistic that would change. There is no clear answer to when Roach -- who played every defensive snap for Oakland last season -- will return.

“That’s something that we continue to look at and see if this is going to get better,” Allen said. “Obviously, number one, any time you have a concussion there’s a concern, and then obviously with the length of time that it’s taken, there’s even a little bit more concern. He seems to continue to get a little bit better every day, and so hopefully he’ll keep getting better.”

The Raiders have clearly missed Roach, as they've given up a league-high 400 rushing yards in the first two games, and would miss Moore, who's been one of Oakland's most active defenders. Miles Burris has been playing for Roach but could move outside for Moore, with Kaluka Maiava playing in the middle in that scenario.

"Well, we’ve got a couple of linebackers that we can use,” Allen said. “So we’ll take the healthy bodies that we have and we’ll have a lineup and put them out there.

Because of the injuries, Oakland is likely to add a linebacker to the active roster Sunday. A likely candidate to be moved up is rookie Bojay Filimoeatu, who was promoted from the practice squad last week, then released, then put back on the practice squad this week.

They made room by cutting rookie defensive lineman Shelby Harris. Harris was a seventh-round pick and is the first draft pick to get cut this season. The Raiders hope to put him back on the practice squad. The Raiders also cut Kaelin Burnett from the injured reserve.