Erick Fedde allowed three runs in a spot start May 23. (Toni L. Sandys/The Washington Post)

Welcome to Minor League Monday, our weekly look at the goings-on around the Washington Nationals’ minor league system. This week, we turn our attention to the organization’s starting pitching depth following the first injury to their rotation this season.

Jeremy Hellickson’s hamstring injury in the first inning Sunday put the Nationals in a bind. After needing seven innings from their bullpen Saturday, the relief corps needed to secure 26 outs for a victory over the Atlanta Braves. They got 24 in a 4-2 walk-off loss. Now, the Nationals need to figure out who will replace Hellickson should he miss time, which will be determined after he undergoes an MRI exam Monday. The good news is, thanks to four off days over the next two weeks, Washington can survive with a four-man rotation until June 19. That could be long enough to avoid having to find a replacement for Hellickson. The bad news is they don’t have many options to fill the spot if they need one.

Edwin Jackson could’ve filled the void, but the veteran right-hander opted out of his minor league contract Friday to look for a big league job elsewhere. Re-signing with the Nationals to join the rotation until Hellickson returns is not out of the question, but Jackson is already considering multiple offers, according to a person with knowledge of the situation. Perhaps he’ll prefer going to a club that could offer a more permanent major league role. The 34-year-old right-hander pitched to a 3.40 ERA in 10 starts for Class AAA Syracuse after posting a 5.83 ERA in 13 outings for the Nationals last season.

Erick Fedde is the likely choice within the organization. The right-hander was solid in a spot start for Washington on May 23, allowing three runs in 5 2/3 innings, striking out six and walking one. Two of the runs were initially ruled unearned after Bryce Harper misplayed a flyball. His stuff looked crisp, with a fastball sitting in the mid-90s. It was an encouraging performance for the Nationals’ top pitching prospect. But the 25-year-old has allowed eight runs on 16 hits across 10 innings since returning to Syracuse. He has logged more than five innings just once in 10 minor league outings this season.

The Nationals have just two other starting pitchers not named Max Scherzer, Stephen Strasburg, Gio Gonzalez or Tanner Roark on their 40-man roster. One, Jefry Rodriguez, is already with Washington. The right-hander was called up Sunday to replace reliever Tim Collins, who was placed on the paternity leave list, and was immediately thrust into a difficult spot for his major league debut. Rodriguez replaced Hellickson in the first inning and tossed 4 2/3 scoreless innings, just three days after throwing 87 pitches in a start for Class AA Harrisburg. He surrendered four hits and tallied four strikeouts. His fastball touched 97 mph. He was impressive in keeping the Nationals in the game.

Rodriguez, 24, was put on the 40-man roster in November after being suspended 80 games for testing positive for a performance-enhancing substance. In 10 starts for Harrisburg this season, the 6-foot-6 Dominican has a 4.33 ERA with 51 strikeouts to 20 walks in 52 innings.

Austin Voth, the other starter on Washington’s 40-man roster, has been called up from Syracuse to the majors twice this season but has yet to appear in a big league game. The 26-year-old had a hot start with Syracuse, allowing two runs in his first five starts with a velocity hike from last season. He then gave up 17 earned runs across seven innings in his next three starts before righting the ship in his past two outings. He owns a 5.10 ERA and is striking out 10.1 batters per nine innings.

For all their injuries this season, the Nationals, until Sunday, avoided one to their rotation. That unit kept the team afloat in April and fueled its surge in May. It boasts the best ERA in the National League. It is Washington’s backbone. And Hellickson has fit right in since replacing A.J. Cole, pitching like anything but a No. 5 starter who signed a minor league deal in mid-March. But injuries are inevitable over a season. Now, the Nationals’ depth could be tested.

Read more on the Nationals:

Daniel Murphy does not look ready to return to Nationals

Max Scherzer wins second straight NL pitcher of the month award

Saturday: Scherzer delivers in a pinch, and Nationals hang on to beat Braves in 14 innings

Friday: Nats are punchless — and nearly hitless — in second straight loss to Braves

Thursday: Nationals step up in competition and falter in loss at Atlanta