The 18-year-old youngster has impressed with his Olympiakos's displays since the start of the season as he continues to be linked with a move to several European clubs.
Monchengladbach are believed to be among them as a scout from the German club will attend Karaiskakis Stadium on Thursday to watch Retsos in action in the Greek Cup semi-final between Olympiakos and AEK.
Goal newspaper understands that Monchengladbach keep close tabs on Retsos who has also been linked with European giants such as Manchester United and Bayern Munich.
