Gregory suffered a thumb injury during Sunday's game against the Steelers. Collie also left that game with a knee injury and did not return. Bolden has been on the team's recent injury/practice reports with a knee injury, but it hasn't forced him to miss any games.
Defensive end Rob Ninkovich, who left Sunday's game with a foot injury and did not return, was on the practice field, as was cornerback Aqib Talib, who has missed the last three games with a hip injury.
There were also two unidentified Patriots, perhaps a signal that some roster announcements are forthcoming. A wide receiver (wearing jersey No. 16) and a running back (No. 35) were taking part in the workout.