The 41-year-old Ramirez, who has racked up 555 home runs and 1,831 RBI in 2,302 games in 19 major-league seasons, was assigned to Class AAA Round Rock, the Rangers said.
Ramirez was to report to the squad Thursday for workouts before being activated.
The controversial and colorful outfielder retired from baseball two years ago to avoid a 100-game suspension for a second violation of MLB's performance-enhancing drug policy. He also was slapped with a 50-game suspension in 2009.
This season, Ramirez has been playing baseball in Taiwan, where he batted .352 with eight homers, 13 doubles and 43 RBI for the EDA Rhinos of the Chinese Professional Baseball League.
Ramirez has played for Cleveland, Boston Red, Los Angeles Dodgers, Chicago White Sox and Tampa Bay. The Dominican Republic native last played in the major leagues with the Rays in 2011, batting .059 with one RBI in five games.