"You are always worried when you are not getting results - and I've been worried for a long time," said the Blues boss.
"We've had a few games in the Premier League where we've not scored enough goals and Tuesday was the same.
"Our performances have not been too bad, but we just can't score.
"In the first 20 minutes at Brentford we probably should have been two or three up.
"We had so many opportunities, but didn't take them and gave them encouragement."