McFarland, a 27-year-old lefty, was placed on the DL on June 30, retroactive to the day before, with left knee inflammation.
McFarland, who last pitched in a major league game on June 28, is 2-2 with a 5.63 ERA in 15 appearances for the Orioles this season. He completed a rehab assignment Thursday, appearing in five games across three minor league levels.
McFarland said: "Initially I obviously wasn't expecting a two-month DL stint, but that's kind of what you run into when you have an injury like that. However long it took, it needed time to get right, and I gave it ample time to do that, so I'm happy."
To make room for McFarland, Baltimore designated right-hander Logan Ondrusek for assignment off the 25-man roster. He was recalled from Double-A Bowie on Thursday, when he pitched one inning in Washington, allowing 3 runs on 4 hits. Ondrusek has a 9.95 ERA in seven relief appearances for the Orioles this year.