The two Brazilians face Xhaka in Group G with both countries eager for a win that will confirm qualification to the Last 16.
Xhaka said: "We were joking before the World Cup to come here and of course, it is always good if you have team-mates opposite your, but we are professional footballers and for 90 minutes.
"I told Gabby Martinelli and Gabby Jesus if you are running one against one against our goalkeeper I will smash you!
“It doesn't matter that we are playing in the same team. This is the Word Cup. You play for your own team, you play for your own country and you want to win.
"Of course, they were worried. They know me. If I smash you, it will be very very hard."