(Shawn Thew / EPA)

The Nationals will place left-hander Ross Detwiler on the 15-day disabled list with the same slight strain in his right oblique that caused him to miss his previous start. The Nationals have yet to determine who will start in Detwiler’s place Tuesday, but they recalled lefty reliever Xavier Cedeno to take Detwiler’s spot on the active roster.

After Detwiler strained his oblique May 15, the Nationals held off on placing him on the DL in hopes he would miss only one start. They scheduled him to start Tuesday against the Orioles, and he remained on track until Sunday morning, when he went through fielding practice and still felt stiffness in his side.

“It’s a lot better than it was,” Manager Davey Johnson said. “It’s tight. He and we didn’t feel like it was the best thing [to start Tuesday]. We’re not going to rush it and exacerbate it at this point.”

Detwiler met with team physician Wiemi Douoguih, and the Nationals expect Detwiler to miss another week. His next start would come next Sunday in Atlanta against the Braves.

By hoping Detwiler could return Tuesday and not placing him on the disabled list shortly after he left his last start, the Nationals effectively played with a 24-man roster for 10 games.

Johnson said starting Jordan Zimmermann on three days of rest on Tuesday will not be an option. Last Monday, lefty reliever Zach Duke started in place of Detwiler, with Craig Stammen backing him up. Johnson said Duke will again be an option.

Before he left his start May 15 in Los Angeles after three innings, Detwiler had been one of the Nationals’ best starters. The 27-year-old has a 2.76 ERA over 45 2/3 innings with 23 strikeouts and 10 walks.

The Nationals claimed Cedeno on April 23 off waivers from the Houston Astros.  With the Astros this season, Cedeno appeared in five games and allowed eight runs over 6 1/3 innings. The Puerto Rico native has made 52 major league appearances over the past three seasons, even collecting a save last year.  In 10 appearances for Class AAA Syracuse this year, Cedeno has a 1.74 ERA with 14 strikeouts and three walks.