The Pirates placed right-hander Juan Cruz on the restricted list and selected left-hander Doug Slaten from Triple-A Indianapolis prior to their Monday afternoon game against the Reds.
Cruz returned home to the Dominican Republic to attend to some personal business that had apparently been festering for a while.
"It's something that came to a crossroads for Juan; it was time for him to get involved in a personal matter," said Pirates manager Clint Hurdle, who anticipates the right-hander's return for this weekend's series in Milwaukee.
Slaten, who was signed by Pittsburgh as a Minor League free agent on Jan. 17, is 2-0 with eight saves and a 0.36 ERA in 20 Minor League games (25 1/3 innings) this season.
Through Sunday, he owned the second-lowest batting average against (.161) among International League relievers.
"He's earned this opportunity; he finally got in shape in early April," Hurdle said of the 32-year-old veteran, who had a 9.00 ERA for six Spring Training appearances with the club. "The last month, his bundle of work has been very clean. We felt he deserved this opportunity in Cruz's absence."
In six Major League seasons -- four with the D-backs and two with the Nationals -- Slaten is 7-8 with a 3.60 ERA. He made 31 appearances out of the bullpen for Washington last year.
Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak.
This story was not subject to the approval of Major League Baseball or its clubs.