Ted Ginn has a right ankle sprain and was rehabbing it at the start of practice on Thursday.
The last time Brandon Jacobs played was on Aug. 18 in a preseason contest against Houston, when he sustained a left knee sprain.
Neither Ginn nor Jacobs are currently listed as the starters or even members of the second-string units, with Mario Manningham, Michael Crabtree and Randy Moss all listed higher on the WR depth chart, and Frank Gore and Kendall Hunter firmly entrenched as the 1-2 punch for San Francisco.
Also, NaVorro Bowman returned to practice. He's back on track to play.
For the Lions, Calvin Johnson practiced in full after taking Wednesday off due to a foot issue. Cornerback Chris Houston was limited, while cornerback Bill Bentley, safety Louis Delmas, defensive end Lawrence Jackson and linebacker Travis Lewis were out.