The 21-year old produced a late challenge on Brockie in the 1-1 draw between the two clubs on the weekend, forcing the New Zealand international off the pitch.
Brockie will now be sidelined for up to 10 weeks which may disadvantage his chances of making the All Whites' World Cup squad and Zullo felt for him when he heard the bad news.
"It's definitely affected me," the Roar utility said.
"I've never been the type of player that goes out to injure people. It's usually been me on the receiving end of those types of things.
"This is his livelihood. You never want to injure someone like that, and he's obviously very talented and has a chance to go to the World Cup, so hopefully he can recover in time.
"Of course I felt worse when I found out his leg was broken. The fact he had to go off was bad enough but to hear his leg was broken was shattering."
Zullo revealed he sent Brockie a text message to apologise and wish him all the best and the New Zealander responded well.
"I sent him a text to make sure he knew how sorry I was and to wish him all the best in his recovery," Zullo added.
"He said there were no hard feelings, but I can understand if he's frustrated and upset with me."