Rivas was designated for assignment by the Angels on Tuesday, Sam Blum of The Athletic reports.
The Halos needed to free up a spot on the 40-man roster for the addition of Robert Stephenson. Rivas was claimed off waivers a month ago by the Angels and will now go through the waiver process again. The 27-year-old has slashed .243/.324/.349 over parts of three big-league seasons.