According to Sport Bild, several figures within Borussia Dortmund were open to bringing Sancho back to the club, with Hans-Joachim Watzke among those believed to have favoured another reunion with the England winger.
Book, however, took a different view.
The new Dortmund sporting director is reported to have used his veto against the proposed signing, delivering a blunt assessment of Sancho’s potential value to the squad.
“He cannot help us! Topic closed,” Book is reported to have said.
The decision prevented Sancho from making a third spell at Dortmund.
The 26-year-old first joined the German club from Manchester City as a teenager and developed into one of the most influential young attackers in European football during his time at Signal Iduna Park.
Manchester United eventually paid €85 million to sign him in 2021, ending a period in which Sancho had established himself as a Bundesliga star and England international.
His career since leaving Dortmund, however, has been far less settled.
Sancho struggled to establish himself consistently at Manchester United and subsequently spent periods away from the club. He returned to Dortmund on loan during the second half of the 2023-24 season before moving back to England.
His Manchester United contract expired at the end of June, leaving Sancho without a club.
Dortmund therefore had an opportunity to reunite with a player who had enjoyed the most productive period of his senior career in Germany.
Instead, Book reportedly decided that the club should look elsewhere.
The decision illustrates the influence the new sporting director is already prepared to exercise over Dortmund’s recruitment. Rather than allowing the familiarity of Sancho’s previous success at the club to determine the decision, Book is reported to have concluded that the winger would not provide what the current squad requires.
Sancho’s departure from Manchester United means his next move remains unresolved, but Dortmund are no longer expected to provide the destination.
The winger’s first spell at the club remains the benchmark for what he achieved in Germany. Between 2017 and 2021, Sancho became a key player for Dortmund and helped establish himself as one of Europe’s most exciting attacking talents.
His subsequent struggles have made a return to the club an increasingly complicated proposition.
Dortmund’s internal debate ultimately ended with Book’s veto, despite reported support for the move from other figures at the club.
Sancho must now continue his search for a new club elsewhere, while Dortmund move forward without the player who once left the club for €85 million.