Rosario was outrighted to Double-A Somerset on Saturday.
Rosario was claimed off waivers by the Yankees on Saturday and optioned to Double-A Somerset.
The Red Sox designated Rosario for assignment Wednesday, Alex Speier of The Boston Globe reports.
Rosario (leg) is slashing .254/.373/.286 with no home runs and two stolen bases through his first 16 games at Double-A Portland.
Rosario left Wednesday's spring game against the Twins with an apparent leg injury, Pete Abraham of The Boston Globe reports.
Rosario's contract was purchased by the Red Sox on Friday.
Rosario went 2-for-5 with a run Wednesday for Low-A Fort Wayne at Great Lakes.