The Red Sox designated Ciriaco for assignment on Monday when they activated third baseman Will Middlebrooks from the disabled list. The 27-year-old infielder hit .216 (11-for-51) with one home run and four RBIs in 28 contests for Boston this season. He saw time at first, second, third base and shortstop.
In 135 career games for the Red Sox and Pirates, Ciriaco has hit .287 with three homers and 30 RBIs.
Darnell batted .246 in 15 contests for Triple-A Tucson this year. In 25 career big league games in 2011-12, Darnell posted a .226 average with two home runs.
Zack Meisel is a reporter for MLB.com. Follow him on Twitter @zackmeisel. This story was not subject to the approval of Major League Baseball or its clubs.