The Germany international has firmly established himself as one of the hottest prospects in Europe thanks to a campaign that has seen him score 16 goals in 41 appearances.
The 21-year-old is expected to command a fee of over £80million if Leverkusen decide to sell the attacking midfielder.
But Chelsea may have received a small windfall that could help them fund any potential deal.
In an official statement on Wednesday, Brazilian club Atletico Mineiro confirmed that they were signing Blues midfielder Nathan on a four-year deal.
Nathan initially joined the Brazilian club on a loan deal in 2018, with renewals made every season since. With his latest loan expiring at the end on June, Atletico have been in negotiations over a permanent transfer.
And according to Globo Esporte, the Brazilians are paying a fee of £2.7million to seal the move.
Chelsea signed Nathan for £3.61million deal from Athletico Paranaense in 2015, but the midfielder failed to make a single senior appearance.
The 24-year-old has enjoyed loan spells at Vitesse Arnhem, Amiens, Belenenses un Portugal and finally Atletico Mineiro, where it looks like his long-term future lies.