Arthur, 21, is set for a move to Barca after his club, Gremio, reached an agreement with the La Liga side, who are set to purchase the midfielder for a reported €40million.
The Brazil youth international is excited to play, and train, alongside five-time Ballon d'Or winner Messi.
"When I started, it was a dream to play alongside players as big as Messi," Arthur told El Larguero.
"Now, it turns out that I will be able to work with him every day.
"Also, I will be able to check if he is from this planet or not because he's an outstanding player."
Arthur made his senior debut for Gremio in 2015 and has already been part of winning the Copa Libertadores, Recopa Sudamericana and Copa do Brasil.
He attracted interest from the world's biggest clubs, confirming Barcelona's rivals Real Madrid also made contact.
"If I don't get confused, my representative did have some unofficial contact," Arthur said. "But no offer came officially."