The Netherlands international is set for a lengthy spell in the treatment room, after undergoing surgery on a knee injury he picked up against Olympique de Marseille
Thursday's Group C encounter at Borussia Park earned Lucien Favre's men their first European victory, but it came at a high cost as the Dutchman crumpled under a challenge from Joey Barton in the 64th minute.
The 22-year-old had to be stretchered off, and further investigation revealed a bone oedema in his left knee cap that required surgery on Friday.
While the operation went smoothly, the former Twente forward is now expected to spend an extended period recuperating, leaving Favre without the striker for up to six weeks.
De Jong is die Fohlen's joint top scorer in the Bundesliga, having scored twice in seven appearances following his move to Germany during the summer.