Gronkowski was seen doing agility drills with a trainer for the first time all training camp, and looked smooth and relatively healthy as he returns from back surgery. Gronkowski, wearing shorts and a T-shirt, ran short sprints forward, backward, and sideways inside a group of cones, and also caught and threw passes with his trainer. Gronkowski had surgery June 18 to repair a herniated disk, and it is unclear when he will be ready to play in the regular season. The rehab for his surgery is generally about 12 weeks, which puts a potential return date right around the season opener. Gronkowski reportedly is unlikely to play early in the season — after facing the Bills, the Patriots’ second game is against the Jets on a short week — but he could potentially be ready to play in Week 3 against the Buccaneers on Sept. 22.