Abbott, 26, has 24 points (seven goals, 17 assists) in 46 games with the Toronto Marlies of the American Hockey League this season. He has played in one NHL game this season and is a unrestricted free agent after this season.
Abbott will report to Rockford.
Brennan, 25, has 36 points (nine goals, 27 assists) in 54 games with the Rockford IceHogs this season. He was acquired in the trade that sent Nick Leddy to the New York Islanders, and represented the IceHogs in the AHL All-Star Game this year.