He was placed on unconditional waivers Thursday despite his ability to handle the knuckleball that had made him Tim Wakefield's personal catcher for several years.
The Boston Herald reported on its Web site that Mirabelli confirmed he had been released.
Mirabelli was supposed to start in Thursday's game against the Tampa Bay Rays. He told the Herald that he was informed he had been scratched from the lineup during batting practice, while Wakefield, the pitcher Mirabelli almost exclusively caught for, was throwing to catcher Kevin Cash in the bullpen.
The skill Cash showed in catching Wakefield's knuckleball last year makes him the likely replacement for the 37-year-old Mirabelli. Cash is 30.
Mirabelli hit a career-high .281 in 2004 when Boston won its first World Series title in 86 years. But he batted just .191 in 2006 and .202 last season.
Cash batted .111 in 12 games with Boston last year.
Mirabelli has a .231 career batting average with 58 home runs and 206 RBIs in 14 seasons. In 2007, he appeared in 48 games, collecting 23 hits and striking out 41 times in 114 at-bats.
The Associated Press contributed to this report.