Matsuzaka's first assignment was cut short last week when he had to get a shot in his right trapezius muscle.
When he pitches against Toledo on Saturday, the clock will re-start at 30 days, meaning the Red Sox must activate him -- barring another setback -- by June 25.
Matsuzaka is coming back from Tommy John ligament transfer surgery. In five Minor League starts this season, Dice-K is 0-2 with a 4.62 ERA.
What do the Red Sox need to see from Matsuzaka before putting him back in their rotation?
"I think it's more hearing it from him," said manager Bobby Valentine. "He's got to know that he's ready, ready to do it. And I don't know when that comes with guys who are rehabbing, but they know. When the time comes, they know."
Matsuzaka isn't the only Major Leaguer playing at Pawtucket this weekend. Outfielder Darnell McDonald was set to play five innings there Friday night as he recovers from a right oblique strain. McDonald will get Saturday off. He is eligible to be activated Sunday, but the team might opt for him to get some additional at-bats in the Minors before he returns.