Donaldson (shoulder) will begin his rehab assignment Saturday, serving as designated hitter for High-A Dunedin, Gregor Chisholm of MLB.com reports.
Donaldson threw the ball around the infield earlier Friday, clearing the final hurdle to begin his rehab assignment. The 31-year-old has been on the disabled list since April 11 with shoulder inflammation, and it's unclear how long of a rehab assignment he is expected to require.