Hart would have become a free agent after the end of the World Series, along with Seattle's other pending free agents, so the move just speeds up his process of being able to negotiate with teams.
Seattle's other free agents will be pitchers Joe Beimel and Chris Young, outfielders Endy Chavez and Chris Denorfia, catcher Humberto Quintero and designated hitter Kendrys Morales. Outfielder Franklin Gutierrez also becomes a free agent after spending the year on Seattle's restricted list following his decision to not report to camp last February.
Hart, 32, hit .203 with six home runs and 21 RBIs in 68 games after signing a one-year deal. The two-time National League All-Star spent a good part of the season on the disabled list with a hamstring strain and then knee issues after missing all of 2013 with the Brewers following microfracture surgeries on both knees.
Montero, 24, was on an injury rehab assignment with Class A Everett for a strained oblique muscle when he got into a verbal altercation with Mariners scout Butch Baccala at a Northwest League game. The Mariners then placed him on the suspended list for the remainder of the season.
Baccala was pulled off his scouting duties at that time by general manager Jack Zduriencik and has since been dismissed by the organization.
Montero spent most of the season with Triple-A Tacoma where he batted .286 with 16 home runs and 74 RBIs in 364 at-bats in 97 games. He played six games for the Mariners and had one home run and two RBIs with a .235 average in 17 at-bats.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.