Naby Keita is due to join Jurgen Klopp's team on July 1 next year after the Reds agreed a club-record £48 million deal to bring the 22-year to Anfield.
But it was not a simple process of negotiations, as RB Leipzig chief Mintzlaff revealed Liverpool had to fend off competition from Barcelona last August.
"FC Barcelona were interested in Naby Keïta," Mintzlaff told German outlet 'Sport Bild'. "That was confirmed to us also from Barcelona. However, they had apparently not given as much gas as Liverpool."
The Bundesliga outfit initially maintained their stance of not selling the player, before a move in 2018 was agreed for the Guinea international to join Liverpool instead of the Catalan giants.
"Naby was very much enthralled by Liverpool and especially by Jurgen Klopp," he added. "It is understandable that he thought this through because he can earn many times what he got from us."
"He wanted to change immediately. But Ralf Rangnick told the team that we will not sell a player [at this time]. It was not lip service, it was carved in stone. We act credibly. Had we released Keïta, other players might have come up with a similar idea."