Blanco lost the fifth outfield job to rookie Jarrod Dyson, and because he was out of options had to go through waivers before he was sent to the Minors.
In Spring Training, Blanco hit .233 in 17 games. Last season with the Royals, he had a .274 average in 49 games after being obtained in a trade with the Braves.
Catcher Lucas May, also out of options, was designated for assignment. He was bumped off the Opening Day roster when the Royals acquired catcher Matt Treanor from the Rangers.
The Royals also formally added pitcher Tim Collins to the 25-man Opening Day roster. He had made the club earlier, but he was not officially moved onto the roster until after Wednesday afternoon's workout at Kauffman Stadium.
Catcher Jason Kendall, recovering from shoulder surgery, was placed on the 15-day disabled list retroactive to March 22 and is expected to begin a rehabilitation assignment in the Minors soon.
The Royals have 39 players on their 40-man roster.