Kottas has been a member of the Greek junior national teams. With Greece's junior national teams, he played at the 2012 FIBA Europe Under-16 Championship, and both the 2013 and 2014 FIBA Europe Under-18 Championships. He also played at the 2015 FIBA Under-19 World Cup, the 2015 FIBA Europe Under-20 Championship, and the 2nd division 2016 FIBA Europe Under-20 Championship Division B, where he won a bronze medal.