[2] After recording a career high 10 points, Brennan was signed to an AHL contract with the Lake Erie Monsters for the 2011–12 season.

[3] Upon his return to the Monsters, Brennan was a main fixture on the blueline appearing in a career high 74 games.

A free agent into the 2012–13 season, and now classified as a veteran, Brennan belatedly signed a contract with the Florida Everblades of the ECHL on November 5, 2012.

[4] After 9 games with the Everblades, Brennan made a return to the AHL, when he was loaned to the Worcester Sharks on November 27, 2009.

On June 21, 2013, after 310 games in the AHL, Brennan signed his first European deal; a one-year contract with the German club Iserlohn Roosters of the Deutsche Eishockey Liga (DEL).