The Belgium international has not found the back of the net since September but the Villa boss feels that his return to the side will have a big impact on his side.
"His return is a boost, as is his presence," he told reporters.
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"He will have spells where he doesn't perform and his confidence will suffer along with every other young player. They lose confidence quicker than experienced lads.
"If he comes back and does what he did at the turn of the year last year, he will kick on again and have another massive impact. It's against Sunderland again, which is where he kicked in last year. His presence is a big factor."
Lambert also refuted suggestions that the striker had been brought back into the side too quickly after struggling with a succession of injuries.
"No, he did not come back sooner than he should because he felt good," he stated. "You can only put him out there and see if he's good. It wasn't until a few weeks ago he felt a bit of pain.
"Hopefully that's cleared up now. I think he will be okay."