The Sky Blues boss believes that his side became submissive in the second half and did not show enough spirit.
"We lost our way a bit. We stopped doing what we work towards all the time, our passing became a bit lethargic and we didn't keep passing the tight areas like we normally do," he told the club's official website.
"In the end we went down 2-0 and on reflection Brentford deserved that but the one thing that disappointed me was the way we lost our spirit.
"That's not the type of performance I want. In football you are going to lose games and there is a manner to lose them and today we looked like we just accepted that."
Coventry lie in 22nd place in League One with four points on the board, having started the season on -10.