Stanley spent four years in the Tigers' minor league organization. In 1962, he played for the Duluth Dukes in the outfield with Jim Northrup and Willie Horton—a trio that later played together in Detroit for more than a decade. Stanley's speed and fielding talents impressed, but his failure to hit for average delayed his progress to the big league roster. He hit .252 with the Knoxville Smokies at Double-A level in 1963. He began the 1964 with the Triple-A Syracuse Chiefs, but he hit only .160 in 19 games and was sent back to Knoxville 50 at bats with Syracuse where he hit a career high .304 in 90 games.