The Marlins optioned Blalock to Triple-A Jacksonville on Monday, Christina De Nicola of MLB.com reports.
Blalock was acquired from the Rockies in January after he was DFA'd by Colorado. The 25-year-old right-hander has appeared in 21 career regular-season games at the MLB level, making 18 starts, but has turned in an 8.16 ERA, 1.83 WHIP and 47:43 K:BB across 89.1 innings.