Barry Robson reckons Duk is ready to recapture his form of last season after scoring for the Dons in the Europa Conference League in Greece.
The Cape Verde international striker was joint top scorer for Aberdeen last season with 18 goals alongside Bojan Miovski.
But while the North Macedonian international has soared this season and has become their main striker, Duk has struggled to return to top form.
His opening goal in Thessaloniki against PAOK was only his third of the season.
But Robson is sure the goal will see him kick on.
He said: "We know what’s in there. I believe in him more than anyone. He knows that.
"Form dips now and again but that is football, it happens to everyone.
"People tend to forget that even in the games when he is not scoring he is still really contributing to the team.
"He is still winning penalties and can do things in our team that no-one else can.
"And that is why he will play a big part for us this season.
"Bojan has been flying and Ester Solker is a really good mover. It is so frustrating for Ester to try to get on the pitch as well.
“You can see what we are trying to build."
Aberdeen were eliminated from the group stages with two games to go despite an excellent battling draw in Greece.
But Robson insists ahead of their trip to face Celtic in Glasgow tomorrow his players deserve plenty of credit.
He said: "We haven’t come out with what I thought we deserved and that is the biggest frustration.
"I don’t care what anyone says, you have to realise when you see that the quality we are coming up against.
"We need to gain more experience to get better in Europe. The more you play in Europe the better you get at it.
"The players have a taste for Europe. It is really difficult to get into the group stages, and into Europe at all.
"All the Scottish teams we are fighting against, it is really hard, especially at the minute.
"The message I want to put out there is that I am so proud of how the players have performed in Europe.
"This is a new group who have not had a lot of time with each other. But they have fought so hard in Europe and are in a cup final.
"We will buckle down, keep fighting and moving forward.
"All I want is for my players to get credit. We are in here in Europe fighting for Scotland. We are in a cup final, playing PAOK, Frankfurt and are away to Celtic on Sunday.
"I’m proud of my players.”
Meanwhile, PAOK have returned fire on Aberdeen's allegations that their sub Papa Gueye was racially abused by their fans during the game.
They stated: "The claim is clearly a product of imagination, as it did not come to the attention of any official.
"There has never been racist behaviour in our stadium and it would not be tolerated anyway.
"Instead, the defiant behavior of the Aberdeen substitutes in their equaliser was evident and to their credit the fans did not react at all."
