Mario has signed to the end of the season.
He told whufc.com: “I was at the Euro 2016 final when Portugal played France, so I had an opportunity to watch Joao there.
“He can play in a number of roles. There's a little bit of Manuel Lanzini about his play. He could play off the left or right and even as a No10 if needed.
“I hope he will be a player who will create and score a few goals for us. Even before Manu's injury we were looking to add some creativity but now the need for that type of player is even more acute.
“At the start of the window the move didn't look like it would happen but as the days have gone on it became more likely."
Moyes admits Mario will need to hit the ground running.
He added: “The hardest thing about bringing players over from other countries is them having to adapt to the tempo of the game here.
“I would hope that Joao can adapt quickly because we need him to hit the ground running. We will need to ask for some patience in getting him settled but our situation means we will need to get him involved quite quickly."