The transfer is set be completed, when the summer transfer window opens on June 1.
The media have allegedly spoken to anonymos sources at Leeds who claim that the transfer could be worth up to €9million (£7.7m; $9.026m).
Sources at the German club say that the fee will be €6m (£5.1m; $6.8m) guaranteed, with potential add-ons.
Frankfurt signed a loan deal for Rasmus Kristensen in July last year and the Danish international right back, who faces Tottenham in the quarter-final of the Europa League on Thursday, has since made a name for himself in the Bundesliga.
Former Leeds defender, Robin Koch, along with two other player, have played more minutes than Kristensen in a successful season where Frankfurt are in contention for a Champions League spot as they are currently third in the Bundesliga.
The former Red Bull Salzburg defender still has two years left of the five-year contract he signed, when Leeds paid around £10m ($13.2m) for him in 2022.