With third baseman Manny Machado's suspension looming, the O's opted to keep utility infielders Paul Janish and Ryan Flaherty rather than play four games without a backup infielder on the roster.
"We are going to be short somewhere regardless," manager Buck Showalter said. "That's part of the penalty. Kind of pick your poison."
In his most recent stint with Baltimore, McFarland, who was last recalled from Norfolk on June 1, threw four scoreless outings sandwiched around an appearance with five earned runs allowed on June 11. In 13 games with the O's this season, the 27-year-old is 1-2 with a 5.