The fee is the second-highest received by an Allsvenskan club so far during the current transfer window after Bazoumana Toure left Hammarby for German Bundesliga club TSG Hoffenheim earlier this month for €10 million.
Qasem is the latest player to depart The Yellows this winter, as the squad which impressed in the UEFA Europa League (UEL) this season fell short of qualifying for the knockout stage.
Having navigated three rounds of qualifying, Elfsborg picked up 10 points from their eight league phase fixtures, recording wins against Roma, Qarabag and OGC Nice.
21-year-old Qasem started all eight matches and scored his first goal in European competition proper in the 1-0 win over Qarabag, adding to two goals he notched in the qualifying rounds.
In total, the Elfsborg academy product contributed 11 goals and 13 assists in 89 appearances for the club from Boras.
Perhaps the biggest loss for the Swedish club - and the biggest gain for Nashville - will be Qasem's versatility.
Predominately a right-winger, he has played no fewer than eight positions in his fledgling career, ranging from defensive midfielder to centre forward, and has also operated on the left flank.
Elfsborg losing attacking talent
The UEL results were a bright point for Oscar Hiljemark's side, who finished seventh in the 2024 Allsvenskan, five places lower than their 2023 showing.
Despite additions this winter of centre-back Rasmus Wikstrom, plus midfielders Simon Olsson and Julius Magnusson, they are yet to strengthen in attack.
As well as Qasem, they have also sold Ghana international and two-time UEL goal scorer Michael Baidoo to Plymouth Argyle in England.
Putting the ball in the back of the net was one positive for them last season; of the six teams who finished above them in the league, only champions Malmo FF bettered their tally of 52 goals.
Reinforcements before the transfer window closes next month may be key to Elfsborg mounting a title challenge in 2025.
