Castillo missed time earlier in the spring after straining his oblique. The 27-year-old signed a seven-year, $72 million deal with Boston last August, then played in 10 games down the stretch. In 36 at-bats, he hit .333 with two home runs and six RBIs.
This spring, Castillo is hitting .310 with two home runs and five RBIs in nine games.
Bradley, 24, started 111 games for the Red Sox last season, including 105 in centerfield. He hit .198 with one home run, 30 RBIs and a .265 on-base percentage.
Boston opens the season in Philadelphia against the Phillies on Monday.
- Molly Geary