Rivers was acquired by the Orioles on Wednesday as the player to be named later to complete the trade that sent Tanner Scott and Cole Sulser to the Marlins.
Baltimore also received Antonio Velez and Kevin Guerrero, with Rivera being the final piece of the deal. Rivera started 12 games at rookie ball last year and had a 3.69 ERA, 1.33 WHIP and 35:14 K:BB over 39 innings.