"Hopefully it's nothing serious," assistant general manager John Ricco said. "It may be nothing."
Ricco said Montero did not complain of the soreness immediately after his start, but alerted trainer Ray Ramirez to it later in the evening. Montero, 24, has not had any notable shoulder or arm injuries since signing with the Mets as an undrafted free agent in 2011.
If healthy, he will report to Las Vegas to continue working as a starter. The Mets could tap him for another spot start later this summer, or insert him into the rotation if another pitcher suffers an injury.
Already this season, the Mets have lost starting pitcher Zack Wheeler and reliever Josh Edgin to elbow surgeries. Top prospect Noah Syndergaard dealt with some forearm soreness earlier this spring, while relievers Bobby Parnell and Vic Black have suffered setbacks in their respective injury rehab programs. The Mets are also without relievers Jerry Blevins, who has a fractured left forearm, and Jenrry Mejia, who is serving an 80-game performance-enhancing drug suspension.
Montero is 1-4 with a 4.14 ERA over 15 career big league appearances, nine of them as a starter.
Anthony DiComo is a reporter for MLB.com. Follow him on Twitter @AnthonyDiComo and Facebook. This story was not subject to the approval of Major League Baseball or its clubs.