"Contact will be made in that area, there's no doubt about that."
But McGahan, who coached Irish club Munster to win the Celtic League title in 2010-11 before joining the Australian camp this year, believed Genia was up for the added attention.
He said at Munster he used to cut up video clips of Genia to show up-and-coming No 9s how they should aspire to play.
"Working with him in this environment over the last few weeks you can certainly see what a competitor he is and what high standards he has on himself and brings out in the team.
"We were greatly enhanced by his role there on Saturday night."
McGahan said the Welsh enjoyed the "fractured part of the game" so the Wallabies were expecting their opponents to rely more heavily on their kicking game after a change in tactics made an impact in the second half of last Saturday's test.
"That's where they'll come at us; the contact area defensively and a strong kicking game will be their second platform."
- AAP