Though everyone is focused on the receiver position for the Patriots at the moment, what's going on defensively may have a bigger impact on Sunday's game with the Lions.

Trey Flowers was missing from the start of practice for the second consecutive day, per reporters on the scene. Flowers suffered a concussion against the Jaguars in the first quarter of New England's Week 2 game down in Jacksonville, and he did not participate in Wednesday's session.

Patrick Chung was also missing from practice Thursday after he sat out Wednesday's practice with a concussion of his own. He did not return to the field after the Patriots headed to the locker room for halftime against the Jaguars.

Rex Burkhead made a quick return to play after dealing with a concussion last week -- he saw 14 snaps in Jacksonville -- but he was on the field for both Wednesday and Thursday's practices last week.

Should the Patriots be without Flowers and/or Chung, the defense will have to adjust as they are two of the most active players on that side of the ball for Bill Belichick.

Along the front, the Patriots could activate Derek Rivers for the first time this season to give their edge-defender group some depth. Rivers has been a healthy scratch and still has not played in a regular-season game since being drafted out of Youngstown State in the third round last year.

A torn ACL robbed him of his rookie season, and as a member of one of the team's deepest position groups this year he has not yet made an appearance in uniform. Though Rivers doesn't appear to be the well-rounded player the Patriots have in Flowers -- who has proven to be effective as both a pass-rusher and a run-stuffer -- he is a good athlete who could give the Patriots pass-rush a boost.

At safety, the Patriots figure to use Devin McCourty and Duron Harmon heavily. They like their "big nickel" package with Chung healthy, but if he can't go, Brian Flores may call upon a more traditional nickel look with three corners. That could mean more time for Jonathan Jones (as it did last week), Jason McCourty or rookies JC Jackson and Keion Crossen -- both of whom have been inactive for the first two weeks of the season.

Chung's injury could further shake up a group that was already going through some changes in Jacksonville. Eric Rowe, dealing with a groin injury, was benched for the large majority of the game, making room for Jason McCourty to see much more time (53 snaps) than he did in Week 1 (one snap).

If both Chung and Rowe are limited or out, it would mean the Patriots are rolling without two of their three most-frequently used defensive backs from Week 1. Rowe tied for a team-high 74 snaps that day with Stephon Gilmore, and Chung checked in with 73.