"It was just a little tight," Matz said immediately after that outing. "Once I got out there, it was feeling good. And it still feels good now."
"After his [debut], he was a little stiffer than we liked," manager Terry Collins said Sunday. "He's fine, as you saw. That's what that first start does to you -- all of that adrenaline and trying to overthrow a little bit."
Yet Matz felt enough continued discomfort this week for the Mets to schedule an appointment at the Hospital for Special Surgery in Manhattan. There, Matz received his diagnosis and a platelet-rich plasma injection.
Because the Mets have been employing a six-man rotation, either Jon Niese or Bartolo Colon can easily slide into Matz's slot Sunday against the D-backs on normal rest, with Niese, who beat the Giants on Monday, the most likely candidate. But the situation is still concerning for Matz, whose injury history includes Tommy John surgery in 2010 and complications from that procedure.
The Mets' top-ranked prospect and No. 54 in baseball, according to MLB.com, Matz did not break camp with the team, but posted a 2.19 ERA in 15 outings at Triple-A Las Vegas with more than a strikeout per inning. That created significant fanfare for his debut at Citi Field, where Matz threw 7 2/3 innings of two-run ball, drawing more attention for his bat -- he went 3-for-3 with four RBIs at the plate -- than a left arm that delivered fastballs as swift as 96 mph.
Sometime between then and his next start, Matz felt discomfort in his lat. But he answered the call at Dodger Stadium, again impressing with six shutout innings.
Now, Matz's short-term future is in doubt, at least until doctors reexamine him three weeks from now.
Anthony DiComo is a reporter for MLB.com. Follow him on Twitter @AnthonyDiComo and Facebook, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.