 On 26 October 2018, Retsos is available for selection again and was on the Bayer Leverkusen bench in a UEFA Europa League match against FC Zurich.On 29 November 2018, after a very difficult period for the defender marred by injury (208 days to be exact), Retsos returned to action in a UEFA Europa League home game against Ludogorets, but was unlucky as in the first half hour left the pitch with a muscular injury on his left thigh and according to the initial reports, Retsos will now spend another 10-12 weeks on the sidelines.On 29 October 2019, after a second very difficult period for the defender marred by injury (334 days to be exact), played in a DFB-Pokal game as a substitute in a 1–0 home win against Padeborn.