BALTIMORE -- The Phillies acquired left-handed reliever Fabio Castro from the Rangers on Thursday for Double-A starter Daniel Haigwood.

Castro, 21, went 0-0 with a 4.32 ERA in four appearances with Texas this season. Opponents batted .200 against him, though he issued seven walks in eight innings. He's expected to join the Phillies on Saturday in Toronto, at which time a roster move will be made to fit him on the 25-man roster.

"Fabio is someone we've had our eye on since before the Rule 5 Draft approached last December," assistant general Ruben Amaro said in a statement. "He has a quality arm, is young and someone we're pleased to have in our organization. We feel that he has a chance to develop into a setup-type reliever, which has become more and more valuable over the years."

A native of the Dominican Republic, Castro was selected by Kansas City in December's Rule 5 Draft from the Chicago White Sox and then immediately traded to Texas. He began the 2006 season with the Rangers before being designated for assignment on June 24, giving the club 10 days to make a roster move regarding his status.

Haigwood, 22, is a former 18th-round draft pick and was 2-5 with a 3.54 ERA in 15 starts for Double-A Reading, allowing 72 hits and 42 walks in 84 innings, while striking out 85. He was one of three players acquired from the White Sox in the November trade for Jim Thome.