The Cardinals signed Fuentes, 36, to a Minor League contract last Saturday with the intention of having him spend some time pitching in the Minors before joining the big league club. Fuentes reported to Jupiter, Fla., on Sunday to begin his throwing program under Cardinals supervision.
Fuentes pitched the first inning of Friday's GCL Cardinals' game. He allowed a leadoff single before inducing a double play and inning-ending groundout. Fuentes is scheduled to make at least one more appearance with the GCL team.
The Cardinals have the option to leave Fuentes in the Minors only until the end of the month. Fuentes' deal includes an opt-out clause that he can trigger if he is not added to the Major League roster by July 31.
Fuentes, a four-time All-Star, was released by Oakland earlier this month, following a string of seven appearances in which he gave up 13 runs. The Cardinals' pursuit of the veteran reliever was initiated by the need for some left-handed help in the bullpen.