Dante Polvara is injured while Duk (right) is also missing from the Dons squad
Aberdeen say they are taking disciplinary action against Duk after the Cape Verde forward "failed to report to training and is currently absent without permission".
The 24-year-old is not in the Dons squad for Saturday's Premier Sports Cup group-stage opener away to Queen of the South.
Aberdeen had previously said that Duk missed the club’s training camp in Portugal on medical grounds and manager Jimmy Thelin would only say on Friday that his continued absence was because of "internal issues".
But a club spokesman has now explained that Aberdeen had "made attempts to communicate with Duk, but he has refused to engage with us directly".
Aberdeen bring in 'leader' Heltne Nilsen from Brann
Who has your Premiership club brought in & let go?
"He is now subject to internal disciplinary proceedings," the spokesman said.
"We're naturally disappointed with the situation but can't say anything further at this stage."
The former Benfica B player, who is in the final year of his contract, has been linked with a move away from Pittodrie.
As he looked forward to his first competitive game in charge, Thelin said: "With Duk, he is not going to be inside the squad.
"Right now, we have some internal issues about the Duk situation."
Chief executive Alan Burrows recently said Duk, or any other player, will only be allowed to leave if the club's valuation is met.
Dante Polvara is another player Thelin will be unable to call upon, after the midfielder was ruled out for up to 16 weeks after injuring his hamstring in training.
"For us he is an important player, now it is our job to push him," said the new Dons boss.
"He is a really nice guy, positive guy, so we have to create the feeling about the future and support him in this process so he can come back even stronger.
"We have some ideas already on how we can support him but also what he can bring to the team.
"We told him yesterday he is going to be a super expert in offensive set plays now. He is going to be like a coach sometimes and help in training sessions to feel close to the team and important for the team still."
Visit our Aberdeen page for all the latest news, analysis and fan views
Get Aberdeen news notifications in the BBC Sport app
Euro 2024: Build up to final as England look to make history
'Southgate inherited a shambles but now stands one game from greatness'
'England will lift a major trophy soon – but I don't want to wait any more'
Leafing through the incredible science of trees
Brian Cox and Robin Ince discuss the wonder of trees with Dame Judi Dench and guests
Could you put your ego to the side to win a big prize?
In this new game show, five strangers rank their obsessions from worst to best
John McFall: The first Paralympian in space?
John McFall's journey from Paralympic medallist to trainee astronaut
'I think sitting in traffic is great'
What do Lupita Nyong'o and Joseph Quinn make of this Unpopular Opinion?
What now for Clarke as Scotland's ongoing deterioration continues?
'Time for Scotland rebuild? Or can this team reach World Cup?'
Do Scotland's problems lie away from the national team?
From titles to tinpottery – rank Scotland's top 10 clubs
Subscribe & follow updates on your Premiership team
'Southgate inherited a shambles but now stands one game from greatness'
'England will lift a major trophy soon – but I don't want to wait any more'
'De la Fuente knew Spain were special – a nation now agrees'
'Nobody will believe I won Wimbledon – I still can't'
'Goals galore & flying wingers – plenty to fear for England'
'Frawley redemption at heart of famous Ireland win'
Boy prince Bellingham ready for biggest stage
'England fire first Ashes shot, now must make sure it does not backfire'
'England play terrible football' – who do neutral fans want to win final?
Why Mainoo has 'wow factor' – and could be one of the greats
England or Spain? Sutton's Euro 2024 final prediction
Yamal's unbelievable year of records… will he add one more?
England sweep aside West Indies in Anderson farewell. Video
How much do you remember about Euro 2024?
Seven of the best saves at Euro 2024. Video
Hewett fights back to beat Fernandez in thrilling semi-final. Video
'You feel bulletproof' – why Eden Park is the All Blacks' fortress
Penalties, red cards and shocks – England's 58 years of hurt
Beating the press & solo skill – tactical trends of Euro 2024
Will Foden get the better of Rodri? Five key battles
© 2024 BBC. The BBC is not responsible for the content of external sites. Read about our approach to external linking.
