The 45-year-old became the first major managerial casualty of the sea-son after 17 months in charge.
Thorn was tasked with masterminding a return to the Championship and brought in nine players this summer.
But his new-look side surrendered leads against Yeovil and Sheffield United and letting a two-goal lead slip at home to Bury on Saturday proved to be the final straw with supporters booing the players off the pitch at the end.
Assistant manager Richard Shaw and first team coach Lee Carsley will take temporary charge of first team affairs.
“We have not taken this decision lightly,” said Fisher.
“We recognised last season there were off the field matters that affected team affairs and felt it was right and proper to give Andy the chance to put that right over the course of the summer and the start of the season.
“We do not feel that has happened.
“Of course, the fact we have surrendered the lead in the first three league games has not helped but there are several other factors in this decision, not just three disappointing results.
“We would like to put on record our thanks to Andy for his work in current and previous roles at the club.”
Thorn took over as manager from Aidy Boothroyd back in April 2011 after impressing as caretaker manager alongside former assistant Steve Harrison.
He became an instant hit with supporters for his attractive style of play, but as the club’s off-field crisis worsened, so too did the on-field performances and the Sky Blues dropped back into the third tier of English football for the first time since 1964.
Development director Steve Waggott, who has worked closely with Thorn since arriving at the Ricoh in December, hinted that promotion was not looking likely under the leadership of the former Wimbledon and Crystal Palace defender.
“There is no doubting the ability in the squad, you saw that in the first half against Bury and in much of the second half against Sheffield United.
“It’s vital now we all pull together as a club and ensure we start to win matches in the next few weeks.”