Masterson came on in relief on Tuesday night, when Matsuzaka left after one inning with shoulder fatigue. Matsuzaka was placed on the 15-day disabled list the next day.
Francona also announced Friday that Tim Wakefield, coming off a complete game in Oakland on Wednesday, will get an extra day of rest. He'll start Tuesday night against Minnesota.
Matsuzaka and Jed Lowrie will both meet with team doctor Thomas Gill before Friday's game to get a further evaluation of their injuries.