The 27-year-old, signed by Lambert's predecessor Alex McLeish at the start of last season, has bore the brunt of much criticism from the Villa Park faithful since his arrival from Tottenham.
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However, Villa are yet to receive an offer for the former Rangers player, and Lambert isn't sure whether he'll remain at the club for the forthcoming campaign.
"Will he be a Villa player before the transfer window closes? I don't know, I'm not so sure," Lambert told reporters.
"But there have not been any enquiries for him at the minute. He's shown a good attitude in training so there are no qualms on that front."
The former Norwich City boss still hopes to add to his squad before the end of the transfer window, and will sit down with owner Randy Lerner and chief executive Paul Faulkner to discuss new targets.
"As manager you always want to bring in one or two more players," he added.