Holder of a Ph.D. in Sports Science and an HDR (an accreditation to supervise research), Grégory has also played football to national level (Amiens SC, Tournai, FC Dieppe). He then became a coach. In 1999, he joined Lille OSC football team as physical trainer before becoming manager of the Sports Science Department at Celtic F. C. in Glasgow, then Manager of the Performance Department at Lille OSC. In 2017, he joined the French Football Federation as head of the Technical Advisory Management's Performance Unit. He won the 2018 World Cup as a member of that team. Since July 2019 he has been physical trainer for Real Madrid.