Leverkusen sit second in the Bundesliga and have bolstered their squad with the signing of the 20-year-old Ryu.
The forward, who starred for South Korea at the Under-20 World Cup in Turkey this year, will link up with compatriot Son Heung-Min at the BayArena.
Ryu completed a medical in Leverkusen on Wednesday and the club said he would join team-mates at a training camp in Portugal early next year.
Leverkusen also announced they had the option to buy Ryu at the end of his 12-month loan deal.
Ryu was regularly linked with a switch to Borussia Dortmund earlier this year, but a deal did not materialise.
Leverkusen are seven points behind runway Bundesliga leaders Bayern Munich and will play their last match of 2013 at struggling Werder Bremen on Saturday.
Get the best features, fun and footballing frolics straight to your inbox every week.
Thank you for signing up to Four Four Two. You will receive a verification email shortly.
There was a problem. Please refresh the page and try again.