He said: "I don't know why they are not scoring as many. We're also missing Mario's goals. Last season, he scored 13 in the league and this season, he only got one.
"It's clear that we're missing seven, eight, nine goals and if we had got these, we probably would have four or five points more.
"We are disappointed because we lost two points against QPR but there are some games when you can attack for 100 minutes and you don't score."