He was suspended from 22-31 July for not riding out Meaningful, who finished fourth, a short-head behind the third, in the opening EBF Maiden Stakes.
Stipendiary steward Phil Tuck said: "It appeared as if Kevin Darley had stopped riding in the closing stages, and we felt that he could and should have been third."
The race was won by the Howard Johnson-trained Pacific Pride, ridden by Robert Winston.
Darley is considering an appeal and said: "I will be discussing the matter with John Blake, secretary of the Jockeys' Association and take it from there.
"I was only looking after the welfare of the horse in the closing stages - I was worried that something may have been wrong somewhere. If I had reported that when I came in, nothing would have been done.
"I had kept nudging away and it was just instinct that I did it a bit harder when the other horse came alongside. That may have made it look as if I had stopped riding and then started again, but I had not stopped."