Erlein, who stands at 1.90m, signs a contract at Leverkusen running until 2030 and will immediately be loaned out to a 2. Bundesliga club as part of the move, rather than joining up with Carles Martinez Novell's first-team squad this season.
Leverkusen are paying Hoffenheim a fee understood to be around €2m plus bonuses, with the Bundesliga club also securing a 15 per cent sell-on clause that could yield further income depending on how the defender's career develops in the coming years.
Despite recently helping Germany's Under-19s to a runners-up finish at the European Championship, Erlein never made a single senior appearance for Hoffenheim under head coach Christian Ilzer, prompting his decision to seek a fresh start elsewhere. His situation at Leverkusen is not expected to be dramatically different in the short term, with the defender not currently part of the club's immediate plans for the first team either, hence the decision to send him out on loan straight away to continue his development in senior football.
The move continues a busy summer of squad business for Bayer Leverkusen following Alejandro Grimaldo's departure to Atletico Madrid, with the club working through a series of potential departures and incomings as they reshape their squad under sporting director Simon Rolfes ahead of the new Bundesliga campaign. For Hoffenheim, the sale represents a modest return on a player they had hoped might eventually break into their own first-team plans, though the sell-on clause offers the club the possibility of a larger financial benefit should Erlein's career progress as anticipated at his new club.
The defender came through Hoffenheim's academy system and had been considered one of the club's more promising young prospects at youth level, making his departure without a senior appearance to his name a notable loss for the Sinsheim club's development pathway.