The Red Bull Arena giants had earlier rejected three bids from the Reds before finally agreeing on a deal that will see the midfielder join Jurgen Klopp’s squad at the end of the 2017/18 season.
The 22-year old joined Ralph Hasenhuttl’s side from sister club RB Salzburg in the summer of 2016 and a £48 million release clause inserted in his contract.
And the club’s Chief Executive says they had no intention of selling Keita but his release clause was the only reason he was allowed to join Jurgen Klopp’s squad while noting they never expected the youngster to attract such interest.
"We would have never given Naby Keita away if it had not been for the release clause," Mintzlaff told Kicker magazine.
"When we agreed on the clause, we did not presume that only after a few months there'd be a club willing to pay significantly more."