Interest is particularly strong in England, where Manchester United, Manchester City and Newcastle United are all tracking his situation.
His performances in Germany have significantly raised his profile, prompting several Premier League sides to explore the conditions of a deal.
At Old Trafford, recruitment chief Christopher Vivell is understood to be spearheading United's efforts, maintaining regular dialogue with the player's representatives as they assess a formal approach.
Meanwhile, Newcastle, also mentioned alongside Michael Carrick in reports, are considering Nmecha as a long-term option should Bruno Guimaraes depart. Manager Eddie Howe is reportedly open to sanctioning a major investment if that scenario materialises.
However, Newcastle's pursuit could be complicated by the midfielder's preference. Sources indicate Nmecha would find a switch to either Manchester United or Manchester City more attractive, largely due to the likelihood of Champions League football compared with Newcastle's current absence from European competition.
Interest is not limited to England. Bayern Munich and Real Madrid are also monitoring developments closely, keeping the situation under review as it evolves.
Nmecha signed a contract extension in March tying him to Dortmund until 2030, and Transfermarkt currently value him at around 50m euros.
However, Borussia Dortmund are believed to be holding out for a fee in the region of 120m euros, with potential for that figure to rise further depending on future performances.
