Defender Demiral was banned for two matches after making an alleged ultra-nationalist gesture in his team's 2-1 last-16 win over Austria.
During the celebrations of his second goal Demiral, 26, made a gesture associated with Turkish right-wing extremist group Grey Wolves, which sparked a diplomatic row, although the player denied any political motivations.
"We consider it unfair, this ban, because there was not a political gesture. It was interpreted as such but it was just something that was not properly understood," Montella told a news conference Friday.
"It's certainly not a ban that puts the breaks on Turkish pride, quite the opposite -- it will be even stronger.
"It's a symbol of the Turks and the Turks around the world and it will remain just that, tomorrow that pride will definitely be more evident on the pitch, in the stands and with those watching on television."
UEFA said Demiral had violated "the basic rules of decent conduct" and brought football into "disrepute".
Germany's Interior Minister Nancy Faeser warned "the symbols of Turkish right-wing extremists have no place in our stadiums".
Turkey summoned the German ambassador on Wednesday over politicians' reactions to Demiral's celebration and Turkish president Recep Tayyip Erdogan decided to attend the quarter-final in Berlin on Saturday.
If Turkey progress Demiral will also be suspended for a potential semi-final against Switzerland or England.
Italian coach Montella said he had faith in whoever he chose to replace the banned Al-Ahli defender.
"We've got three players suspended with Demiral, but the players who have come in have always played well. I'm pretty calm about that."
Tens of thousands of Turkish fans are expected at the Olympiastadion to support their team, given the great number living in Germany.
"Our fans have been exceptional up to now, they've been passionate and really given us their love... they've always been brilliantly behaved and that's what I expect tomorrow, that level of passionate and good behaviour," continued Montella.
"They must show their Turkish pride, be close to the team and show us that even when having hard times."
The coach said his side, the youngest on average at the Euros, had to manage their emotions well and use them to power them to victory against their more experienced opponents.
"(Some of them) are used to playing these matches, preparing for these matches, and they have a bit of an edge," added Montella.
"We must be able to manage this emotional sphere, to turn the emotions into energy.
"We are younger, we can have more energy and this can give us an edge."
