Arsenal were reportedly forced to fork out Michy Batshuayi’s loan fee to secure a deal for Pierre-Emerick Aubameyang.
Dortmund were reluctant to let the Gabon international leave until they had signed a replacement.
Arsenal confirmed the signing of Aubameyang on Wednesday for a fee of £56m.
According to sources in Germany, the Gunners had to pay an extra £1.3m during the switch to cover Dortmund’s loan fee for Batshuayi.
Aubameyang’s transfer saga had a knock on-effect for the Chelsea striker and Olivier Giroud.
The Gunners originally intended for Giroud to be used in exchange for the 28-year-old, but the Frenchman opted to stay in England for family reasons.
Dortmund then indicated their interest in Batshuayi, but Blues were demanding a hefty fee for their only fit forward.
With the clock ticking, Arsenal offered to cover the amount to ensure the capture of Aubameyang.
The departure of the 24-year-old Belgian allowed the Blues to snap up the signing of Olivier Giroud for £18m.
It is understood that he signed an 18-month deal at Stamford Bridge with the option of another 12 months.
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Batshuayi has now undergone his medical with the Bundesliga giants ahead of a proposed six-month loan deal.
The Belgian is keen for first-team football after falling out of favour under the management of Antonio Conte.