Despite admitting his delight following the Belgian's recent return to training, Lambert has warned the striker that he faces a fight to earn a spot in the side.
"It's a massive boost," the Villa boss told reporters. "He's done all the work we've asked of him and there's been no adverse reaction.
"But we still have to be careful with him, and he knows he's going to have to work really hard to get back in the side right now."
Villa, who are yet to be beaten in the Premier League this season, face Arsenal on Saturday afternoon.