The 38-year-old left-hander has a 6.08 ERA in 38 games this season. He allowed two runs without recording an out in his last two appearances against the Baltimore Orioles. In January the Sox signed Downs to a one-year contract for $3.75 million with a team option for 2015.
Left-hander Eric Surkamp was recalled from Triple-A Charlotte to take Downs' spot. Surkamp has a 4.54 ERA in 14 games, including 11 starts, with Charlotte.