The 22-year-old Ramirez will pitch for Nicaragua in the qualifying tournament. Ramirez appeared in 16 games for the Mariners last year starting eight of them. He finished the season with a FIP of 3.55 and went 1-3 over the course of 59 innings.
He finished the year in the Mariners' rotation and has been pitching in the Venezuelan Winter League. Ramirez is expected to make a run at the starting rotation in 2013.
The four other prospects haven't broken camp in the majors yet. Right-handed pitcher Ivan Julio will play for Colombia and right-handed pitcher Thyago Viera will play with Brazil. Viera will be joined by infield prospects Felipe Burin and Pedro Okuda.
Brazil plays Panama on Thursday and Nicaragua plays Columbia on Friday. The winner of the qualifier goes onto the 16-team WBC tournament in March.