The young midfielder had just arrived at Pride Park on loan from Chelsea, and it didn't take long for him to impress his new teammates.
Mount's excellent campaign with the Rams set up his return to Chelsea, where he has made 41 appearances this term.
"The first training with us left the players thinking: 'Wow, who is this guy?!'" Derby goalkeeper coach Given told Goal. "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. He is just desperate to be the best he can be. 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."