He told the club's website: "Without doubt, Ashley is fulfilling the potential he had during his time at Watford and he has turned in a string of excellent performances.
"When he came here, he took a while to find his feet after scoring on his debut but you can see now his confidence is sky high and he has that ability to go past players.
"I believe he can become a really great player. He came in for a bit of harsh treatment today but he is expecting that and Derby were going to play hard.
"But at the moment his confidence is so high he feels something is going to happen every time he gets the ball.
"In the first half he was starved for a bit of the ball and I don't think he touched it for about 10 minutes but once he started to get hold of it he was a real handful."