The Englishman enjoyed another season with the Gunners first team last year.
Maitland-Niles scored a goal and made two assists after recovering from a calf injury.
The 21-year-old even played in the Europa League final, which the lost 4-1 to Chelsea.
But footage has emerged of the midfielder making a surprising revelation.
In the clip, the Gunners star is playing a game of “Favourites”.
The Englishman is asked a series of questions and has to give short answers.
One of the questions asked is the 21-year-old’s favourite stadium.
And he replies: “Old Trafford.”
This is the home of bitter Gunners rivals Manchester United, who Maitland-Niles helped beat 2-0 in their last encounter three months ago.
The Englishman went on to explain his preference over the Emirates Stadium, Arsenal’s home.
He added: “I just think the fans there are fantastic.
“The noise level and pitch are also great.”
“Sell that traitor”
This footage was shared on the club’s official YouTube channel earlier today.
And the Gunners faithful reacted furiously.
“What about the Emirates,” one supporter said.
“Doing us dirty.”
Another commented: “OK, he just said his favourite stadium played in is Old Trafford. Let that sink in.”
While a third suggested a heavy punishment.
“Sell that traitor,” they said.
And a fourth added: “Is he mad?”
But fans went wild over Ian Wright’s Twitter exchange with club mascot Gunnersaurus.