The midfielder is off contract in June and currently on-loan with Sheffield Wednesday.
Asked if there was still a chance of Gardner forming part of his long-term plans, Lambert said in the Birmingham Mail: "There's still a chance, yes, but it's hard for me to judge him when I haven't seen much of him due to his injuries.
"He's had injuries where it's been long term, with his cruciate and then his back.
"The thing about Gary is he's a really good kid, really nice guy and a really top lad that wants to do well. We have to keep looking at him over the next few months.
"There is scope for something. I'm not dismissing it, I just need to see the progress that he makes when he's out playing.
"He's been really unfortunate with injuries, but I'm not dismissing anything at all.
"We have to see more of him performing at a level where we think he can make an impact here. We'll keep a close eye on him while he's out on loan."
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