Demetri was initially a left-footed winger who came to the attention of football fans in spring 2012 when he scored a stunning goal for Manchester United's Under-17 side in the AEGON Future Cup despite only being an Under-15 at the time. He's quick, tricky and an excellent finisher. In 2014/15 he was tasked with improving on his 2013/14 return of 6 goals and 6 assists.
Unfortunately following an excellent start to the 2014/15 season, Demetri picked up a long-term injury in September 2014 that would keep him out until the new year. His luck didn't continue and 2015 proved to be very stop-start with a few setbacks, his season ended early in March 2015.
Demetri returned for the 2015/16 with the Under-21 side and made his comeback against Rochdale in the [Manchester United 0-0 Rochdale (2014-15 Lancashire Senior Cup)|Lancashire Senior Cup]] in mid July 2015. He was only able to complete the first half and missed the next four months with another injury. He returned to training in November 2015 but had to wait until February 2016 to make his return for the Under-21 side as a substitute away to Manchester City.
In the 2016/17 season, around December, Demetri found himself in a new left fullback position following an injury to Joe Riley. Demetri continued and thrived in that position so much that he was rewarded with his First Team debut in the final game of the season at home to Crystal Palace.
In January 2018 Demetri joined Hearts on loan until the end of the 2017/18 season and followed that up by going on pre-season tour with the First Team in the summer of 2018. Demetri rejoined Hearts on loan for the 2018/19 season.
Demetri was released by Manchester United at the end of the 2019/20 season.