Cuellar reckons the £23.5 million attacking midfielder will be a threat to Villa on Saturday afternoon.
"I am very surprised he has adapted so quickly," said Cuellar. "He is doing so well so quickly. He is already one of the best players in the Premier League.
"I am so happy for him because he is doing brilliantly and impressing the people in this country.
"It usually takes time to settle and show your true quality when you move countries and leagues, but he has settled here so quickly. I am really pleased for him."