Long struck in Friday's defeat to Liverpool.
Bertrand said: “It's good for any of our strikers to get off the mark.
“He worked very hard on Friday and got what he deserved.
“If you look at his commitment, it's never in question.
“He just needs to get the rub of the green sometimes and he got that against Liverpool.
“Hopefully, he can go on and keep that form going now.
“People are always going to talk but as long as you stay mentally strong and believe in your abilities then you can do your talking on the pitch."