Eintracht continued a busy day by bringing in Dominik Kohr from Bayer Leverkusen.
The 25-year-old midfielder has joined on a five-year deal for a reported €10 million fee.
Beaten by Chelsea in the Europa League semi-finals, Frankfurt finished the 2018-19 Bundesliga campaign in seventh place.
They did, however, lose the services of star striker Luka Jovic, who completed a €70m (£62m/$79m) move to Real Madrid in the summer transfer window.
Frankfurt face Hoffenheim in their first match of the 2019-20 Bundesliga season, with the game due to take place on either August 17 or 18.