Gestede scored two of Cardiff's goals and Mackay said that although his performance was excellent, he is still not the final product.
"I loved his attitude when he arrived here," Sky Sports News quotes Mackay as saying. "He wanted to throw himself into everything.
"There are rough edges that have been smoothed out and are being smoothed out, but there are times when he looks unplayable."
Cardiff are six points clear at the top of the Championship.