Mets doctors discovered a tear in Daniel Herrera's left elbow, and the southpaw will undergo Tommy John surgery, a baseball source told ESPNNewYork.com.

Herrera had remained in spring-training camp until the near-end as a hedge against Tim Byrdak not being ready for Opening Day because of March 13 surgery to repair a torn meniscus in his left knee.

Herrera, 27, made 16 relief appearances last season and had a 1.13 ERA after joining the Mets as a player to be named in the Francisco Rodriguez trade with the Milwaukee Brewers. He was removed from the 40-man roster during the offseason and remained with the organization. Herrera had tossed six innings with Triple-A Buffalo this season before the left elbow difficulty sidelined him.

Chuck James is off to a solid start at Buffalo (6.1 IP, 0 R, 1 H, 4 BB, 6 K) and would be a candidate for left-handed relief should an issue arise with Byrdak in-season or the Mets desire a second southpaw in the bullpen. Josh Edgin, who is closing at Double-A Binghamton, has the highest upside and should be in the Mets bullpen in September if not sooner.