This was the first on-field work for Tretter since May 20, when he suffered a broken fibula in a fumble recovery drill and underwent surgery two days later.
"He's got a long way to go but I like what I've seen so far," said Larry McCarren, the team's starting center from 1974-'84 who is permitted to watch every practice in full in his role as analyst on the Packers' radio network.
"He looks like a natural knee bender, and that's where your power comes from. He seems to be technique-orientated; he's not all over the place. He's detail-orientated.
"I think he's probably a center-guard prospect. Just body type."
Mike Trgovac, who coaches the defensive line, took notice of Tretter in May.
"He looks like he can really fit into this scheme," said Trgovac. "I've seen him do some things where I said, 'Wow. He's going to be a good offensive lineman.'"