Mayo's deal was wrapped up in the morning as his teammates embarked on their first practice, and he was expected to be in the field house for the evening workout.
Coach Bill Belichick all-but confirmed that Mayo, a linebacker who was the 10th overall selection, was signed at his mid-day news briefing with reporters.
"It sounds like that's getting pretty close," Belichick said. "But until they're done, to me, they're not done."
The deal was announced a few hours later.
Also on the PUP is offensive lineman Nick Kaczur, who was in court Tuesday in upstate New York dealing with a misdemeanor charge of drug possession.
Copyright 2008 by The Associated Press.