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 to 12 weeks on the sidelines.