In addition to Gregory, running back Danny Woodhead joined running back Shane Vereen and tight end Visanthe Shiancoe as those not spotted on Sunday. Defensive tackle Kyle Love, who missed Friday's session, was back on the field, while offensive lineman Nick McDonald took part in stretching but was in a T-shirt and shorts.
Safety Patrick Chung, who returned to practice on Friday, was in a red jersey for Sunday's session, perhaps indicating that he is not yet cleared for contact. Chung was injured in the team's second preseason game.
Gregory was injured in the third preseason game, in Tampa, but had returned to practice and made the trip to New York for the final preseason game last Wednesday.
Without Gregory, the Patriots were down to Chung and rookies Nate Ebner and Tavon Wilson at safety. Without Woodhead and Vereen at running back, the Patriots had only Stevan Ridley and Brandon Bolden at that position.
With a full week of practice ahead before next Sunday's regular-season opener in Tennessee, it could be too early to read into the status of the players who did not practice on Sunday.
Coach Bill Belichick said Sunday's practice was for situations and points of emphasis. The team will begin its preparations for Tennessee on Monday.
Meanwhile, tight end Aaron Hernandez was spotted walking off the practice field back into the stadium just as reporters were entering. He was not accompanied by a member of the team's training staff, but did not return to the field during the 15-minute media access period.