Derby County coach Shay Given said Mason Mount stunned his Rams teammates upon his loan arrival last season.
The 21-year-old has established himself as a fully fledged first-team player at Chelsea under Frank Lampard this season.
But before his Premier League stardom, Mount had already got plenty of attention during his loan spells.
Given, who is a goalkeeping coach at Derby County, revealed how the England international left a deep impression on his former teammates in his first training session.
The former Newcastle United shot-stopper told Goal: “The first training with us left the players thinking: ‘Wow, who is this guy?!
“We knew about him as a young prospect at Chelsea who had done well in Holland [on loan at Vitesse], but it is not until he is actually on the training ground that you really see what kind of player he is.
“He was some player for us. His finishing, power, pace and work rate was great. Of course, he has played so many games this season for Chelsea and he was one of our best players at Derby.
“Even at Derby, they thought what a player he is going to be from the first training session and he went on from there.”
Mount came to Derby after a remarkable season-long loan stint at Vitesse, where he managed 14 goals and nine assists in the Eredivisie.
Mount’s nine goals and four assists helped Lampard’s Derby reach the Championship play-off final, although they suffered a defeat to Aston Villa in the showpiece event.