Ross Ohlendorf. (Doug Pensinger/Getty Images)

After a successful bullpen session earlier in this week, Ross Ohlendorf will begin his rehab assignment on Saturday at Class AAA Syracuse, according to Nationals Manager Davey Johnson. He will be limited to four innings or about 65 pitches, Johnson said.

On Wednesday, Ohlendorf threw his first bullpen session since experiencing a tired arm on July 31. Ohlendorf threw only 11 pitches that outing and his normally mid-90s fastball topped out at an alarming 85 mph. That was because his arm hadn’t yet recovered from the previous 114-pitch start on July 26, his highest pitch total in four years, and he then landed on the disabled list with right shoulder inflammation.

Ohlendorf is eligible to come off the disabled list on Aug. 16. He has pitched well since joining the Nationals as a hybrid long reliever and spot starter, posting a 1.85 ERA over 34 innings. Right-handed Tanner Roark was called up on Tuesday to fill Ohlendorf’s role in the meantime. Ohlendorf is a candidate to take rookie right-hander Taylor Jordan’s spot in the rotation when he is shut down in about four starts because he is in his first full season back from Tommy John surgery.

If Ross Detwiler returns by September, the left-hander could be reinserted into the rotation. Detwiler has been out since July 4 with a herniated disk in his back. After the diagnosis by Los Angeles back specialist Robert Watkins Sr., Detwiler was told to rest for a month, which means he could be ready to throw again by late August. On Friday, Johnson said Detwiler is improving ahead of schedule but will need to rest the full 30 days.

Detwiler hopes to beginning running in the outfield on Friday or Saturday. Even if Detwiler can begin all activities later this month, he would still have to begin a throwing program and build arm strength, which could take weeks. Johnson said he doesn’t expect Detwiler will need to visit Watkins again to be cleared to resume throwing.

“He’s feeling good,” Johnson said. “In my experience, don’t let him keep poking him. Crank it up, let’s go. We’ll be very cautious with him coming back. I would like him to pitch before the year it out.”