Mario completed his move from Sporting CP last week.
“I am not going to talk about who will play. Joao Mario can start, but almost everybody is fit right now and so tomorrow you'll see who starts," said De Boer.
“I think Joao Mario is a very complete midfielder who can play on the outside, the inside, 4-4-2 and a more defensive midfielder in 4-3-3, but is also a box-to-box player. It's an advantage that we can use him in all aspects of all systems."