The only goal of the game was scored by Erling Haaland, who found the back of the net on Sunday.
Collins, a centre-back, acknowledged that the team was too passive in the first half, allowing City to have too much space and not pressuring them enough.
He felt that the team could have done better with the goal, which he wants to review to see what went wrong.
In the second half, Brentford made some adjustments, pressing higher up the field and creating more opportunities to score.
Although they defended well in their own box and made it difficult for City, Collins felt that they could have created more chances to win the game.