ALLEN PARK — Calvin Johnson, who sat out Wednesday’s practice with a foot injury, was back at work today (Thursday) during the portion of practice that was open to the media.

Still missing from practice were: DT Corey Williams (knee), DE Lawrence Jackson (calf), LB Travis Lewis (quad), S Louis Delmas (knee) and CB Bill Bentley (concussion).

Chris Houston, who practiced Wednesday after missing several weeks with a high ankle sprain, returned to practice today.

The Lions are preparing to play the 49ers at San Francisco on Sunday Night Football.

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