Hamilton (lat) was scratched from his scheduled rehab appearance at Double-A Somerset on Friday due to back spasms, Bryan Hoch of MLB.com reports.
Hamilton has been on the injured list since mid-June due to a right lat strain and would have likely been making his final minor-league appearance before rejoining the Yankees' bullpen. Instead, his activation will almost certainly be delayed, and there's no telling how far away he is from a return.