The Magpies made a concrete enquiry for the Germany international in the closing stages of the window, according to Sport Bild, proposing to offset the transfer fee by including striker Nick Woltemade in the deal alongside a substantial cash payment.
Borussia Dortmund's hierarchy rejected the proposal quickly, regarding Nmecha as one of the most important players in their squad for the season ahead and unwilling to entertain his departure regardless of the makeweight on offer.
Newcastle United's interest in Nmecha had been building for weeks, driven by the need to replace Bruno Guimarães following his move to Arsenal. Dortmund had previously signalled that any sale would require an "astronomical" fee, with reports earlier in the window suggesting a valuation in the region of €100million to €120million.
The swap proposal represented an attempt to bring that number down to a level Newcastle could stomach, but Dortmund's refusal to engage left the Premier League club needing to find a central midfield solution elsewhere.
Woltemade ultimately joined Juventus on loan before the window closed, meaning the player Newcastle had hoped to use as a makeweight ended up leaving Tyneside regardless of the Nmecha deal's collapse.
Newcastle instead strengthened their midfield through other means, bringing in Nico González from Manchester City for a reported €56million, along with Aladji Bamba and Sean Steur, as the club worked to rebuild the department following the departures of both Guimarães and Sandro Tonali earlier in the window.
For Dortmund, retaining Nmecha represents a significant statement of intent given the scale of interest in the 25-year-old, whose contract reportedly contains an €80million release clause that becomes active next summer, a figure considerably below what Newcastle appeared willing to pay this time around.
Dortmund sporting director Nils-Ole Book had played down the prospect of a Nmecha sale throughout the summer, previously describing a transfer as "extremely unlikely" barring an offer of truly exceptional scale.
That stance proved decisive once Newcastle's proposal arrived, with the swap element seemingly doing little to change Dortmund's calculation given how central Nmecha has become to head coach Niko Kovac's midfield plans following his development into one of the club's most important players since arriving from Wolfsburg in 2023.