The Anfield Stadium outfit shelled out £48 million to secure the signature of the Guinea international at the end of the 2017-18 season.
And the German believes the 22-year-old is one of the best talents he has 'worked with in 20 years of professional football' and admitted the Red Bull Arena outfit’s wage structure made it impossible to keep the player at the club.
“He’s one of the best I’ve worked with in 20 years of professional football,” Rangnick told Kicker.
“I’d also prefer, 10 times, that we’d kept him for another five years - but we are just not able to pay salaries in excess of €10m.”
Keita who has been putting in impressive shifts for Leipzig so far this season will join Jurgen Klopp's side when the summer transfer window open on July 1, 2018.