The Portugal international moved to the San Siro on the back of European Championship glory in 2016.
The 24-year-old midfielder has struggled to produce his best in Italy, with little return offered on a €40 million fee.
It has been suggested that he could seek another switch in January, with clubs across Europe expressing an interest, but Spalletti claims to have been offered no indication that will be the case.
The Inter boss told reporters: “As for Joao Mario, he’s a simple lad to understand, he has a wonderful attitude in attending training and in the dressing room. When I’ve talked to him he didn’t tell me anything strange.
“There can be a lot of rumours about a player, they can be true or false but he’s a good lad from a professional point of view.
“I’m sorry that there were a couple of balls he could have scored from and he didn’t take those chances, if you think about leaving you lose a bit of attention in those situations.
“It’s inevitable in that case you lose your motivation for results, application makes the difference.
“So he’s not happy now, but he’s trained well and all I care about is that he’s professional every day and he’s doing that.
“If I saw a blatant bad attitude it’s clear we’d address that problem straight away, because I’d be the first to highlight it.”
Regardless of the rumours surrounding Joao Mario and any one else at the club, Spalletti has warned those planning a winter raid on Inter that the club will not be forced into selling any player they wish to keep.
He added: “A player will leave if we decide he leaves, otherwise he’ll stay and get his head down for two games, because if he thinks about the deadline he’s wasting his own time.
“In January it’s right that those who leave will be the ones we say, not those who want to leave.”