The Marlins recalled Ralston from Triple-A Jacksonville on Sunday.
The right-hander was added to Miami's 40-man roster in early August, and he's now on the cusp of making his major-league debut. Ralston has enjoyed a strong season for the Jumbo Shrimp with a 2.04 ERA, 1.06 WHIP and 76:30 K:BB across 61.2 innings out of the bullpen.