New York Mets starting pitcher Seth Lugo delivers a pitch...

New York Mets starting pitcher Seth Lugo delivers a pitch against the Minnesota Twins during the first inning of an MLB game at Citi Field on Saturday, Sept. 17, 2016. Credit: Kathleen Malone-Van Dyke

Mets righthander Seth Lugo has been diagnosed with a partial tear of the ulnar collateral ligament in his right elbow that ultimately may require surgery, the Mets announced on Tuesday. Sources told Newsday that the Mets believe the injury could be fallout from Lugo pitching in the World Baseball Classic.

Lugo’s injury further depletes the starting pitching depth that the Mets believed would be a strength this season, and it may be enough to trigger efforts to bring in more options.

For now, Lugo does not require Tommy John surgery. Instead, he underwent a platelet-rich plasma injection on Tuesday morning to promote healing. He will rest at least two weeks while the treatment takes effect, though his absence could linger far longer.

Another source confirmed that Lugo’s test results also will be reviewed by Dr. James Andrews, as per standard protocol. If the treatment does not work, Lugo would undergo surgery.

Lugo said on Monday that he experienced tightness in his elbow last season, an indication that he may have been pitching through a pre-existing condition. However, a source said that the Mets believe the UCL tear is a new injury suffered sometime in spring training, perhaps while Lugo pitched for Puerto Rico during the WBC.

Meanwhile, the Mets will be keeping a closer eye on adding starting pitching depth, a source said, though for now they are targeting pitchers to stash away in the minor leagues.

Lefthander Steven Matz is already on the shelf with a strained flexor tendon in his elbow. Along with Lugo, he is on the 10-day disabled list, leaving the Mets with five of their top seven starters healthy.

Righthander Rafael Montero could step in as starter. But he is currently in the bullpen.

The rest of the Mets’ depth at Triple-A includes Adam Wilk and Sean Gilmartin, who was slowed in March with a shoulder ailment.

Lugo was expected to win a spot in the Opening Day bullpen, though he easily could have been deployed as a starter if the need arose. Now the Mets have little margin for error with their starting rotation.

Lugo finished spring training with a 4.78 ERA, though most of those innings came while pitching for Puerto Rico. At the end of camp, Lugo may have aggravated the elbow in a start against the Nationals. He later complained of arm fatigue and the Mets placed him on the 10-day disabled list.

But as recently as Monday, neither Lugo nor the Mets believed that the issue was significant. A second opinion showed otherwise.

Lugo went 5-2 with a 2.67 ERA down the stretch last season, when he stepped in to fill the void as injuries ravaged the Mets’ rotation.