Nationals closer Drew Storen will visit renowned surgeon James Andrews tomorrow for a second opinion on his right elbow, Manager Davey Johnson said.

Storen will almost certainly not need Tommy John surgery, a typical fear when players visit Andrews. But depending on the results of Andrews’s examination, Storen could miss at least half the season because of a loose body in his elbow and the surgery that would be required to remove it.

Storen, 24, felt tenderness in his elbow Sunday while throwing a simulated game, particularly when he threw fastballs. Storen had been rehabbing since early in spring training, when he felt soreness in his biceps and triceps.

“Alarm bells went up on him,” Johnson said. “He had been feeling real good, and they he kind of let it out in that sim game. He had some fallback pain. So we’re going to reexamine. Hopefully it’s nothing serious, but it doesn’t sound good to me.”

On March 22 in Washington, Storen underwent an arthrogram, an MRI in which doctors inject dye into the specified area. The procedure showed Storen’s ulnar collateral ligament, which if torn necessitates Tommy John surgery, had no tears and was structurally sound.

Those test results still gives the Nationals confidence Storen will not require the ligament-replacement procedure. But the test also revealed a “loose body” in Storen’s elbow, Johnson said, which the Nationals did not publicly disclose at the time. They also believed it was too small to pose a problem, Johnson said.

Storen also received an anti-inflammatory shot. When Storen returned from the two procedures, Storen felt no more pain in his elbow.

A pitcher can, and often does, throw with little or no pain with a bone chip in his elbow. But when the bone chip becomes lodged in the wrong place, it causes pain too significant to pitch through. The Nationals hoped the rest and an anti-inflammatory shot would allow the inflammation in Storen’s elbow to dissipate, and that the bone chip would not pose an issue.

“It doesn’t look like the rest and the treatment is helping him,” Johnson said. “It may be something more severe.”

When Storen threw hard Sunday, he felt the same soreness in his elbow return. Whether the loose body in Storen’s elbow is a bone chip or cartilage, it could require surgery to remove. In 2010, then-Nationals starting pitcher Jason Marquis had surgery to remove bone chips in his elbow on May 14. He did not pitch again in the majors until Aug. 8.

Storen, the 10th overall pick on the 2009 draft, saved 43 games last season even after beginning the year as a set-up reliever. He compiled a 2.75 ERA with 74 strikeouts in 75 1/3 innings, never experiencing any issues with arm.

While Storen has become the Nationals’ clear-cut closer and one of the best young relievers in baseball, the Nationals are well-positioned to replace him. With Storen on the disabled list, the Nationals have closed games with Brad Lidge, a 35-year-old veteran with 224 career saves and Henry Rodriguez, who threw the hardest fastball in the majors last year and has harnessed it this spring.

“I felt like last year, we had one of the best bullpens in the National League,” Johnson said. “With the addition of Brad Lidge, we got even more depth. But any time you lose somebody the stature of Storen, that’s a big concern of me. But I love my bullpen. I think it’s very capable. Thank goodness we have enough depth to hold us in there until he gets back.”