The All-Pro has been participating in his side's practice sessions for the past two days after missing all of pre-season due to his recovery from back and forearm operations.
"There is no straight-line formula for that. We take it day to day," Belichick told reporters.
"I don't know any other way to do it. We don't know how he's going to be feeling in two days. Or any other player. It's not about him, it's about any player that's coming back from injury. That's how we do it. Nobody has a crystal ball.
"This is his first opportunity to be in pads. So, yeah, he's definitely moving forward."
New England face the Buffalo Bills in their season opener on Sunday.