"They've got a lot of young guys who are trying to play their way and trying to play really well at this level.
"[It's] dangerous for us ... they back themselves to play from anywhere on the field. They've got that young 'let's have a crack' attitude, which is going to provide opportunities if we're lazy," he said.
Adam Ashley-Cooper ran freely and completed the session seemingly unscathed, but remains unlikely to start after almost two months sidelined with a knee injury.
Grey said it was entirely up to Ashley-Cooper and Cheika whether or not the Wallabies backline ace was ready for a comeback, after last week saying it was most unlikely.
"I seriously don't know. We're definitely hoping to have him back," Grey said.
"We understand the injury and what-not, so it's a matter of if he's 100 per cent ready to go, both from his perspective and the physios."
Grey said the Waratahs would "cross that bridge when we come to it" when asked what Ashley-Cooper's comeback - whenever it may occur - would mean for Israel Folau's roving commission and rights to inject himself from fullback to outside centre whenever he felt like it.
"Obviously the opportunity to play Israel up in the front line has its positives and also if you've got someone like Adam coming back into the side, that provides another opportunity to use him in that part of the field.
"It gives us a few options around the ability to change things up, which keeps the opposition guessing."
"So that's something we can definitely do if it's available to us. But we don't know that yet."
Folau is cool either way. "I'm just happy to fill the positions that I'm required to play. It'll be a huge game for us and if Adam comes back this week, it will be a huge bonus."
- AAP