The French forward, who was once crowned Bundesliga Player of the Year, has endured a difficult spell at Stamford Bridge, scoring only six goals in 36 Premier League appearances and frequently being omitted from Enzo Maresca's matchday squads.
Chelsea's recent signings of exciting forwards Pedro and Jamie Bynoe-Gittens have further limited Nkunku's prospects, effectively accelerating his expected departure.
He did manage to score in Chelsea's Club World Cup last-16 victory over Benfica on Saturday, but the club has now made him available for transfer and is prepared to take a loss on their initial investment, hoping to recoup around 35 million pounds.
Nkunku is reportedly open to a return to Germany, though it remains unclear whether Bayern Munich - who had considered a January move - will revive their interest.
In the Premier League, Manchester United, Arsenal, and Tottenham Hotspur have all expressed interest. United held talks with Nkunku's representatives last month, although they have since signed Matheus Cunha and are focused on securing Bryan Mbeumo.
Arsenal approached Nkunku earlier this year, with Mikel Arteta eager to strengthen his attacking options despite already sealing deals for Martin Zubimendi, Christian Norgaard, and Kepa Arrizabalaga.
Tottenham also held discussions last month, and manager Thomas Frank may revisit a move, especially if he misses out on Mbeumo to United.
Arsenal have confirmed the signing of Spanish goalkeeper Kepa Arrizabalaga on a three-year contract, seven years after he joined Chelsea in what was then a world-record transfer for a goalkeeper.
Former Chelsea wonderkid Charly Musonda has announced his retirement from professional football at the age of 28.
Marcus Rashford's future at Manchester United remains uncertain as Bayern Munich have emerged as contenders to sign the England international this summer, following Aston Villa's decision to pass on a permanent deal.
Tottenham Hotspur have made Mohammed Kudus a key summer transfer target, with the north London club weighing up a 60-million-pound bid for the West Ham attacker.
