Earnshaw, who has netted eight league goals this season, is usually deadly in front of goal had three clear-cut opportunities versus the Robins on Monday to kill the game off.
However, he failed to take any of them meaning Forest had to hang on for their 3-2 win which kept them in the final npower Championship play-off spot.
Chambers told the Nottingham Evening Post: "It is not like him to miss chances like that. But we will allow him one or two, because he has been very good for us lately. Some of his finishing has been brilliant.
"He will get chances again in the coming weeks and I would back him to put them away for us. He might have missed a few at Bristol City, but we all know what he is about.
"If he does get another chance, you'd expect him to put it away. That is what he does."
Source: PA
Source: PA