AC Milan signed Nkunku from Chelsea for around €37m last summer, but the 28-year-old has been placed on the transfer list after failing to establish himself as a first-choice option, scoring eight goals and adding three assists in 35 appearances across all competitions.
The France international was left out of Milan's squad for a pre-season friendly against Manchester United and has himself pushed for an exit, with a loan seen as the most realistic route given his significant salary.
Barcelona have long admired Nkunku's profile, according to L'Équipe, and see him as a potential replacement for Ferran Torres, who is completing a move to Paris Saint-Germain worth around €50m.
A return to RB Leipzig, where Nkunku scored 70 goals and added 56 assists in 172 appearances between 2019 and 2023 before his move to Chelsea, is also considered possible, while Borussia Dortmund have emerged as a fresh suitor after abandoning their pursuit of Köln winger Said El Mala.
Dortmund are also monitoring Genk's Giannis Konstantelias, with David Blacha, a senior figure in the club's sporting department, having watched the Greek winger in a Europa League qualifier against Anderlecht this week.
Sources at the club have all but ruled out a reunion with former player Jadon Sancho, rating the chances of his return at less than one per cent, as Dortmund continue exploring multiple options to strengthen their forward line before the transfer window closes.
For Milan, resolving Nkunku's situation is part of a broader clear-out under head coach Rúben Amorim, who has also made teammate Youssouf Fofana available after the midfielder attracted interest from Nottingham Forest and other Premier League clubs.
Milan's own market has been relatively quiet by comparison, with Gonçalo Ramos, Mario Gila and Sankhoun Diawara their main additions so far, and any funds recovered from Nkunku's departure would likely be redirected toward further reinforcements before the window closes.
AS Roma have also made contact over Nkunku, according to reports in Italy, adding a fourth serious suitor to a list already led by Barcelona.