Uwe Rosler was disappointed with the decision to award Peterborough a penalty in Brentford's 2-1 defeat in the Johnstone's Paint Trophy.
Bees debutant Raphael Calvet was adjudged to have fouled Nathaniel Mendez-Laing in the box 20 minutes before the end, but Rosler believes a penalty should not have been given.
He said: "Raphael did very well on his debut against one of the best teams in League One and I feel sorry for him about the penalty.
"I have checked on the DVD and he clearly played the ball. I'm very disappointed with the decision.
"It would have been easy for the lads to feel down after falling 2-0 behind but we responded very well and had a real go at Peterborough.
"We are conceding too many goals which are coming too easy to our opponents. We need to shore things up."