Brunner won both the European Under-17 Championship and Under-17 World Cup with Germany in 2023, beating France in the final of each tournament. Unable to establish himself at Dortmund, he moved to Monaco in 2024 in search of regular first-team football.
The French club paid around €4 million for the striker before sending him on loan to Cercle Brugge, their Belgian partner club. Brunner scored six goals in 28 appearances there, but his progress then stalled.
Last season he remained with Monaco and made only seven appearances, playing just 127 minutes.
The situation has changed dramatically this campaign. New Monaco coach Filipe Luis quickly installed Brunner as a regular starter and the 19-year-old has responded with six goals in seven matches.
He also carried that form into Germany Under-21 duty, scoring twice in a 4-0 victory over Latvia.
Brunner is under contract with Monaco until June 2028, but Dortmund are continuing to monitor his development.
Sky Germany journalist Patrick Berger said on the Auffe Süd podcast that there could be a mechanism allowing Dortmund to bring their former player back to Germany.
“Two sources within the club have told me that a buy-back option for Brunner by Dortmund is theoretically conceivable,” Berger said.
“Dortmund are already involved in one way or another, we just don't know the details yet,” he added.
Borussia Dortmund sporting director Lars Ricken recently admitted that the club had not forgotten Brunner, while stopping short of suggesting that a return was imminent.
“I don't know if he could have developed as much with us, even with the excellent strikers we had in his position. And then he chose a different path,” Ricken said.
“He's a great guy. Even at Dortmund, we sometimes hear stories about him, but he has always performed on the pitch. The doors are not closed for Paris. But I don't think that's the problem at the moment.”
Dortmund are not currently short of options at centre-forward, with Serhou Guirassy and Fabio Silva providing competition and Maximilian Beier also able to fill the position.
Brunner’s rapid emergence at Monaco, however, means Dortmund are keeping a close eye on a player who could yet return to the club where his senior career began.