The Catalan club moved quickly in recent hours, first securing an agreement with the player himself - a straightforward process given Adeyemi's desire to join and his existing relationship with Hansi Flick from their time together with Germany.
Barcelona then opened talks with Borussia Dortmund, offering €20m in fixed fees plus variables, but the German club rejected the proposal on Thursday, wanting to at least recoup the €33m they paid for the forward a few years ago.
Dortmund's position is complicated by the fact that Adeyemi's contract expires in a year, raising the risk of losing him for nothing if no agreement is reached.
Barcelona remain optimistic. The two sides are expected to continue talking in the coming days, with the Catalans believing Dortmund will ultimately need to sell rather than risk losing their asset for free next summer. That contractual leverage is the card Barcelona are hoping to play as negotiations continue.
Even so, sources at the club stress there would be no great drama if a deal cannot be struck within Barcelona's set parameters. Adeyemi would not arrive to be a guaranteed starter, with Lamine Yamal occupying his position and Roony Bardghji currently the back-up option, even if the Swede has made clear he wants more minutes and has not ruled out leaving himself.
Flick would ideally like to have Adeyemi available for the start of first-team training, though with sessions beginning next Monday, that timeline already looks difficult to meet.
Other reports have suggested Dortmund's true valuation could be as high as €40m, a figure Barcelona have already made clear they are not prepared to reach.
According to Fabrizio Romano, Barcelona will not enter a bidding war and are instead banking on Adeyemi's contract situation to bring Dortmund's asking price down closer to their own valuation over the coming days, rather than escalating their own offer significantly beyond what has already been tabled.