Toronto FC say they offered fired coach Aron Winter a new role within the club, but the Dutchman declined.
Director of player development Paul Mariner has taken over, becoming the club's seventh head coach in just six seasons.
TFC managed only seven wins in 44 Major League Soccer matches under Winter, including a league-record 0-9 start to 2012.
"It was a difficult decision for both of us but one I believed was necessary given our team's regular season results," Maple Leaf Sports and Entertainment Ltd. chief operating officer Tom Anselmi said in a media conference.