Casemiro has told ESPN Brasil that Real Madrid have no problem playing tough against Barcelona if they need to ahead of their International Champions Cup meeting in the United States.
Zinedine Zidane's side face Barca in Miami on July 29 as part of an International Champions Cup summer schedule which also includes games against Jose Mourinho's Manchester United in Santa Clara on July 23 and Pep Guardiola's Manchester City in Los Angeles on July 26.
The clash at the 65,000-seater Hard Rock Stadium will be just a second ever overseas meeting of the two La Liga giants, and International Champions Cup organisers Relevent Sports are organising a week-long build-up of events, which include a "Combate Clasico" Mixed Martial Arts fight night in Miami.
Asked about the controversies that often surround games between the two teams, Casemiro said that the players were friends off the pitch, but each side did what was required to win the game once it began.
"The off-pitch stuff does not affect the game," he said. "But if we need to get stuck in, we do that. If we need to play, we can do that too. We can be friends off the pitch, like when [Brazil teammate] Dani Alves was at Barca, but out on the pitch each one defends their own side."
Casemiro had a difficult time against Messi during the most recent Clasico at the Santiago Bernabeu in April and came close to a sending off.
"[Messi] likes to drive the opponent crazy," Casemiro said. "It is something we talked about in the dressing room. We cannot forget about him as then he makes it difficult for us."
Tickets for the Clasico on July 29 are sold out, with reports claiming fans are paying up to $10,000 to get a seat for the game.