(Alex Brandon / AP)

Ross Detwiler will be placed on the disabled list with discomfort in the left side of his lower back and Dan Haren will rejoin the Nationals rotation Monday in Detwiler’s place, Manager Davey Johnson said.

The decision comes as no surprise after Detwiler felt stiffness in his lower back earlier Saturday as he threw a bullpen session. Detwiler missed a month earlier this season with a strained right oblique, an injury that appears to be unrelated, although Detwiler could have strained his back overcompensating. In five starts since returning from the disabled list, Detwiler has gone 2-3 with a 6.31 ERA.

“He’s a tough customer,” Johnson said. “But he understood the value of getting by this thing. He got a whole of treatment today. And so hopefully we can get by, he’ll be good coming back after the break.”

The Nationals had planned to bring back Haren on Tuesday at Philadelphia, but his schedule will fit him pitching Monday instead. Haren threw an encouraging simulated game Wednesday at Nationals Park. He went on the disabled list June 26 with right shoulder inflammation, which may have contributed to his league-high 6.15 ERA.

Haren was told after the Nationals’ 5-4 victory today over the Padres that he would come off the DL Monday, the first day he is eligible. Haren will pitch against the Phillies, the only franchise he has yet to earn a win against in his 11-year career.

For now, rookie Taylor Jordan will remain in the Nationals’ rotation and make the third start of his career Tuesday in Philadelphia. Jordan has a 2.70 over 10 innings in his first two career starts.

Detwiler will be eligible to come off the disabled list July 19, the first day after the all-star break.

As noted earlier, the Nationals are considering trading for a starter to augment the uncertain back of their rotation.