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"If we can take that away from them then we're a step towards winning the game."
Former Leicester prop Castrogiovanni endured a torrid return to Welford Road in December as Toulon lost out 25-21.
The 33-year-old Italy tighthead stormed into the post-match press conference demanding to set the record straight over his acrimonious Leicester exit in 2013.
Cult figure Castrogiovanni claimed regular rugby not money drove his move to Toulon, but his explicit language landed him a €10,000 fine.
While Ireland respect Italy's fervent approach, McGrath adm itted the pack at least in Schmidt's side will aim to use that passion to their own advantage.
McGrath also conceded he must be on the money against 107-cap Castrogiovanni, while tipping Ross to cope despite limited rugby at Leinster in recent weeks.
"Castro's been there and done that, he has every trick in the book," said McGrath. "But with Rory (Best) beside me and Rossy on the other side I'm confident we can go in and do a job and cause a bit of damage.
"I've been watching Castro for years, he's the guy any young tighthead would look towards. He's the type of guy you've got to respect but you've got to go in and make him respect you too I suppose.
"Mike is looking well, he's an experienced guy, he knows he's ready.
"The coaches have trust in him that even though he maybe hasn't played in the last few weeks he's in position to put it in there, and he's well able for it."