Matz received platelet-rich plasma therapy during an examination by team doctors at the Hospital for Special Surgery on Thursday.
"It's never really pain. It's just like a little pulling. It's hard to describe," Matz said Friday.
Both manager Terry Collins and Matz had acknowledged the southpaw was dealing with stiffness in the lat area by his left armpit between his first and second major league starts. Matz nonetheless proceeded with a second start this past Sunday against the Los Angeles Dodgers. He tossed six scoreless innings at Dodger Stadium.
"It was not the phone call we wanted to receive," Collins said. "It's just another bump in the road we've got to get through and have somebody step up."
Matz became the fifth pitcher in franchise history to earn a win in each of his first two major league appearances. He joined Dick Selma (1965), Gary Gentry ('69), Roger McDowell ('85) and Mike Pelfrey (2006).
Matz also has five RBIs in two major league games.