Eugene Gerard told the Daily Record: "He is going to be big, I'm sure. He has the conditions required to be a great footballer but most importantly he has the desire.
"His move to Celtic is very good for his career because he will play more games than in England and can feel important again, just as he was at Heerenveen. He is going to play for titles and will enjoy the Champions League.
"He is on loan and I will not be surprised if Celtic try to secure his services full-time.
"Georgios is playing at the top level and I am sure there is more to come. If he does well with Celtic maybe he will attract big clubs in Spain or Italy - and that would be hard to turn down."