Fred Jackson, C.J. Spiller not practicing

ORCHARD PARK, N.Y. -- Buffalo Bills running backs C.J. Spiller and Fred Jackson did not participate in the portion of practice open to reporters on Wednesday.

Jackson was on the practice field but not wearing a helmet. Spiller wore a helmet, but pulled out of individual drills to work with the strength staff.

Spiller also missed last Wednesday's practice before returning on Thursday.

In addition, linebacker Manny Lawson (hamstring) and quarterback EJ Manuel (knee) were not spotted when reporters were present.

Marrone had previously said he hoped that Lawson would be back to practice Wednesday "on a limited basis."

Meanwhile, the Bills shifted their secondary look for their walkthrough at the beginning of practice. Aaron Williams and Jairus Byrd aligned as the safeties, with Leodis McKelvin and Stephon Gilmore at cornerback. Jim Leonhard, who has started at safety, was part of the scout team.