The 18-year-old centre-back signed a new contract running until 2029 in March. Since then, however, he has struggled to build on the progress that had raised hopes of a more prominent role with the senior side.
Reggiani has made just two first-team appearances this season, totalling 50 minutes. He was then left out of the squad for Saturday's goalless draw against Union Berlin and instead played for Dortmund's reserve team in the Regionalliga West.
According to Kicker, Borussia Dortmund have doubts about whether the Italian defender has the quality to meet the club's long-term expectations at senior level. A departure during the winter transfer window is therefore considered a realistic possibility.
The report suggests discussions about a potential move had already progressed during the summer, although no transfer materialised before the window closed.
Reggiani's situation represents a sharp change from the optimism surrounding him earlier in the year. His performances had put him in contention for greater involvement with the first team, and the contract extension appeared to underline Dortmund's belief in his potential.
The defender has also attracted interest from abroad. Inter Milan and AC Milan have both been linked with the Italy Under-21 international, although there is no confirmed indication of which club might make a formal approach.
Dortmund's asking price has not been reported, leaving the financial terms of any potential deal unclear.
A winter move would give Reggiani the chance to seek more regular senior football elsewhere, while Dortmund would have to decide whether to cash in on a player they recently committed to for several more years.
For now, the immediate challenge is finding a route back into first-team consideration. With his opportunities limited and competition for places fierce, the coming months could prove decisive for the young defender's future at the club.