Palestine record scorer Oday Dabbagh has joined Aberdeen on loan from Charleroi in Belgium, with Duk being sold to La Liga side Leganes.
The Dons have secured an option to buy Dabbagh, who has netted 16 international goals from 45 caps.
Manager Jimmy Thelin described the 26-year-old as a “clinical finisher who has an exceptional work ethic”.
He has played 15 times in Pro League this season, with just four starts, scoring once.
Dabbagh spent two seasons with Arouca in Portugal before his move to Charleroi in 2023.
The Dons have failed to score in any of their last five Premiership matches and have not won in the league since 9 November.
The departure of Duk was announced after the 23:00 GMT deadline, with the fee undisclosed.
The Cape Verde forward joined Aberdeen from Benfica B in 2022, hitting 18 goals in an impressive debut campaign.
In the summer of 2024, Duk failed to report for pre-season training in a bid to force a move. Returning in September, he expressed deep regret.
He featured in 21 games this term, starting 10, with just two goals against Elgin City in the Scottish Cup.
“Duk has spoken for some time about his desire to try and make the next step in his career,” explained Thelin. “When that happens, I want to ensure all our focus is on the players who can drive Aberdeen towards our objectives.”
