The League One side sit at the bottom of the table after recording four defeats and six draws.
The 52-year-old took over the Sky Blues in March last year, eventually guiding the team to eighth in the standings , five points adrift of the playoff places.
Today, in a statement on the club’s official website, Coventry said: “Without a win in the first ten league games, Tony felt on professional level that he was no longer able to take the club forward.
“Coventry City FC would like to thank Tony for all his energy and dedication over the past 18 months. We would also like to wish Tony all the very best for the future and put on record that he will always be welcome at the football club.”
Technical director Mark Venus will take charge of first-team duties for the time being.