Rob Gronkowski at 1st OTA; Dion Lewis back after knee surgery

FOXBOROUGH, Mass. -- New England Patriots tight end Rob Gronkowski participated in Monday's voluntary organized team activities, marking the first time he has been present since media members first watched practice May 26.

In addition to Gronkowski, running back Dion Lewis, who is recovering from November surgery to repair a torn ACL, was back at practice for the first time this spring.

A source previously told ESPN that Gronkowski has consistently been at Gillette Stadium, working behind the scenes as the club took a cautious approach with an undisclosed physical ailment that wasn't considered a long-range concern.

"The biggest value is consistency, going out there and making sure you are still on the same page. You don't want to lose it. Go out there and knock all the rust [off]," Gronkowski said Monday when he was asked the value of being on the field in OTAs.

Gronkowski did not specify why he hasn't been practicing.

Lewis said, as he has progressed to being on the field, "at the beginning, it was a little scary, but every day I get stronger. I feel better every day but still have a long way to go."

Lewis was not wearing a brace over his left knee during practice.

"The trainers wouldn't have put me out there if they didn't think I was ready. I wouldn't have went out there if I didn't think I was ready. ... I wouldn't consider this a milestone," Lewis said. "I wouldn't consider it a checkpoint. I consider it another day working hard and trying to get better and stronger."

It has been commonplace for the Patriots to hold back Gronkowski in recent years after he injured his forearm and knee in 2012 and 2013, respectively. Over the past two seasons, Gronkowski has missed just two games because of injury.