Pen star Lugo hits IL

If the Mets don’t have enough problems, they lost an integral piece of their bullpen to the injured list Monday.

Seth Lugo was placed on the IL with right shoulder tendonitis after experiencing discomfort during his last appearance. The right-hander is 2-0 with a 3.12 ERA in 19 appearances this season and along with Robert Gsellman has been the team’s best setup man this season.

Hector Santiago was selected from Triple-A Syracuse to take Lugo’s spot in the bullpen. Lugo said the injury was similar to discomfort he experienced in 2017 that forced him to miss a start against the Yankees.

With Lugo sidelined, manager Mickey Callaway changed his pitching plans against the Nationals, inserting Wilmer Font in the starter’s role. Drew Gagnon, who was originally slated to start, shifted to the bullpen.

Gagnon pitched scoreless fifth and sixth innings in the 5-3 victory.

“This is the job we have been looking for all year to get the job done and he’s been outstanding,” Callaway said. Michael Conforto has been “symptom free” in recent days, according to general manager Brodie Van Wagenen, after sustaining a concussion last week in a collision with Robinson Cano. The outfielder will continue to be evaluated. It is unclear if he will be removed from the injured list when eligible later this week.

Jason Vargas came through his Sunday rehab start for DoubleA Binghamton without incident, according to Callaway, and is likely to be slotted back into the Mets rotation. Vargas has been on the injured list for the past two weeks after straining his left hamstring.

Anthony Kay is on the Mets’ radar, according to Callaway, but the left-hander wasn’t given serious consideration for a promotion to start against the Nationals on Monday.

In nine starts for Double-A Binghamton, Kay is 5-2 with a 1.07 ERA and 0.77 WHIP, including throwing seven no-hit innings when he struck out seven and walked one on 88 pitches in a 3-0 win over Bowie on Monday.

“We’ve talked a lot about Anthony,” Callaway said. “We do feel that he still needs further development. We love what we’ve seen so far.”