The 23-year-old made a big impression in his debut campaign at Villa Park, bagging 19 Premier League goals, although he has only managed to find the net on four occasions so far this term.
Benteke has not been on the score sheet since September's 2-1 defeat at home to Newcastle and Lambert acknowledges that a hip injury has resulted in a dip in the striker's performances.
"He is having a hard time, but he's still carrying a few knocks," he told the Daily Star.
"He's got a little minor thing that's hindering him a bit.
"The injury was his first one in football, believe it or not. If he can handle it, I'm not so sure, but it's not that he's not trying."
The Belgium international has now gone 10 league games without finding the net, but Lambert is optimistic that the goals will eventually return.
"Maybe it's a little bit of a lack of confidence when things aren't going your way," he said.
"He set himself such a high standard last year that the little knocks he's carrying aren't helping him. It's my job to rectify that.
"He's not in so much pain that he says, 'I can't do this'. It's not that, it's little things that are hindering the movement he has.
"He just needs one to go in. He's definitely not shrunk, but the confidence thing is major. If you're confident, you'll do things off the cuff without thinking about it. Maybe he's thinking too much."