The Australian international was signed in March on a pre-contract from Dutch club AZ Alkmaar when Alex McLeish was at the helm at Villa Park before officially joining on July 1.
Lambert, who replaced McLeish in June, admits he does not know the attacking midfielder all that well but will give him a fair chance to become a first team player for Villa.
"If there is one lad who has probably got a bit of trepidation, then it would be Brett because it wasn't me who brought him to the club," said Lambert.
"But I have spoken to him to reassure him and he will get a right fair chance.
"I don't know much about him but I have watched some of his games. He did well at Alkmaar so I don't have any worries about him on that score.
"It's not as if you are going in with a young kid. He is 28. As long as he works hard and tries to be successful, then he will be the same as everybody. He will get a chance."