Nebraska defensive end Randy Gregory announced late last month he intends to leave school and apply for early entry into the draft.
But while Gregory (6-foot-6, 248 pounds) has a number of desirable traits, he is not a finished product.
Zierlein elaborated on his tweet Wednesday afternoon.
"He doesn't play with the upfield burst you expect, his hands are fairly basic and too often he plays too square, giving tackles a much easier target to block," Zierlein said. "With work and coaching, he could become a really good rusher, but substantial improvement is never a lock or we would never have draft busts."
Zierlein said Gregory's positives mean he will be drafted early.
"The length, the explosive hips and the ability to close quickly are all great traits that will get him drafted early, but I was surprised how raw he was as a pass rusher on tape," he said.
"I have a couple of NFL scouts who are arguing with me about Gregory right now, but they also admit that they are betting on the raw talent and traits, with coaching filling in the holes."
NFL Media analyst Gil Brandt says seven teams drafting in the top 10, including four of the top five, could use a pass rusher, which likely means Gregory -- and others like him -- will receive extra scrutiny from those teams.
Gregory had 17.5 sacks, 29 tackles for loss and 34 quarterback hurries in his two seasons with the Huskers after transferring in from junior college.