Montanez was the third overall pick from the 2000 draft, but has struggled through most of his minor league career, which has spanned seven seasons in the Cubs' system.
Drafted as a shortstop out of high school in Miami, Fla., he converted to the outfield midway through 2004 and then posted modest results at the plate due to a self-described newfound lack of pressure on defense.
A little over a month into the 2006 season, Montanez earned his first career promotion to Triple-A after hitting .369 in 38 games at Double-A. But he still came up short of the 40-man roster and any September consideration.
Sing, who was eligible for six-year free agency a year ago but re-signed with the Cubs for 2006, is fresh off his worst season ever. He combined to hit below .200 between Iowa and West Tenn.
Beginning Sunday, teams may begin to sign players who opted for free agency the previous week. Jackson, Montanez and Sing could still re-sign with the Cubs.