The Red Sox will option Kelly to Triple-A Worcester on Saturday, Chris Cotillo of MassLive.com reports.
The decision to send Kelly down to the minors comes shortly after he allowed three earned runs on a hit and two walks without recording an out in Friday's 5-4 loss to the Yankees. The 29-year-old righty owns a 3.97 ERA through 56.2 big-league innings on the year and could still return to Boston to help the Sox get through the final weeks of the regular season.