The Brazilian centre-back moved to the Emirates Stadium from Villarreal on Wednesday and is expected to make his debut against Aston Villa on Sunday.
Walcott has been impressed with the 24-year-old in training and has no doubt he will be able to handle the physical nature of the English game.
"I've only trained with him once and he likes to put his foot in, that's for sure," the England international told the club's official website.
"He's not afraid to do that which is good, especially in the Premier League where you need to get stuck into your tackles.
"He's very tall - I didn't realise how tall he was. He'll only be tested when he plays in the Premier League.
"It will take time coming from a different country to learn the language, the culture, so everyone will be patient with him.
"Players that the boss plucks out seem to be good players so I'm sure he's going to help us."
Victory for Arsenal over struggling Villa would see them climb back above Tottenham and into fifth place.
