The 23-year-old Greek, only recently signed from PAOK Saloniki for 26 million euros, suffered a cruciate ligament tear in the 2-0 opening win over Hamburger SV on Bundesliga matchday one and will therefore be unavailable to BVB for "several months".
On their official account on X, the Bundesliga runners-up wrote: "The entire BVB family is behind you, Giannis! You will come back stronger!" BVB managing director for sport Lars Ricken said: "This news hits us hard, because Giannis has already shown in a very short space of time why we see him as a great player for Borussia Dortmund. For now, however, his and our focus is first and foremost on his recovery. Giannis has our full support in that."
Konstantelias, who marked a strong Bundesliga debut with a goal, twisted his knee in an innocuous challenge early in the second half. Although he was able to leave the pitch under his own steam after lengthy treatment, the body language and facial expressions of the player and staff offered little cause for optimism.
Getty ImagesHow do BVB replace Giannis Konstantelias?
For Dortmund, the question now is simple: how do they replace Konstantelias? One thing is certain, those in charge at BVB will be working overtime again in the few remaining days before the summer transfer window closes on Tuesday (1 September) at 8pm.
Ricken had already hinted at that on Saturday evening: "Depending on how serious the injury actually is, we will shape our next steps accordingly. One thing is certain, though: we won't be doing nothing over the next three days."
One internal solution could be the currently very dissatisfied Fabio Silva, who has recently been repeatedly linked with a swift exit after just one season in Dortmund. But Konstantelias' injury is likely to have put an end to that.
Jadon Sancho, still without a club, could meanwhile once again become a serious option in the plans of the BVB bosses. The Englishman would be a natural solution, is a similar type of player to Konstantelias and, like him and Konstantinos Karetsas, has the quality to create dynamism from a standing start.
Getty ImagesBVB: Jadon Sancho would be available on a free transfer
Speculation over another Sancho return to BVB has not gone away in recent weeks and months, although it died down after the signings of Karetsas and Konstantelias.
At Dortmund, Sancho enjoyed the best spell of his career so far. After his contract expired at Manchester United, the now 26-year-old remains without a new club and would be available on a free transfer.
That makes it a low-risk move, although Sancho would have to be prepared to accept a significant pay cut for a third spell with Borussia. There is also the sporting question of whether the former super talent can ever hit top form again. As is well known, his recent loan spells at Chelsea and Aston Villa were largely disappointing.