[1] Before moving to Bundesliga, Ryu showed his credentials on the international stage, scoring a couple of goals to help South Korea into the knockout round of the 2013 FIFA U-20 World Cup in Turkey.

[3] Bayer Leverkusen's skipper Simon Rolfes praised Ryu for his "intelligent play, good movement and use of space.

"[4] On 25 January 2014, Ryu made his first official Bundesliga debut against SC Freiburg, substituting his South Korean compatriot Son Heung-Min in the second half.

[12] He was called up for South Korea's 21-man squad for the 2013 FIFA U-20 World Cup in Turkey, and scored the winning goal against Cuba in the side's opening match of the tournament.

On 27 June 2013, Ryu was injured and substituted during South Korea's final game of the group stage against Nigeria, forcing him to miss out their Round of 16 match against Colombia, and subsequently, their quarter-final loss against Iraq.