Derbyshire was on fine form, grabbing a well-taken double in the 4-1 destruction of the npower Championship side at the New Den.
"Matt has been waiting for his opportunity. He played in a couple of Carling Cup games but looked a little short of fitness in the first few months, but those goals will do his confidence the world of good," said McLeish.
"Strikers thrive on confidence and he will benefit from that. He did well with his first goal and it was great to see it nestling in the back of the net."
Derbyshire's loan from Olympiakos is due to expire at the end of the season but McLeish was non-committal on the hitman's chances of making his move permanent.
He said: "He is on loan until the end of the season. I have been waiting for the strikers to settle from the start of the season.
"We have worked hard and I cannot fault them with their efforts but they have been unfortunate with the finishing side of things.
"I believe there are goals in this side and Cameron and Matt showed that today.
"Cameron is normally worth 10-12 goals a season. He just needs a little break."