Jockey Paul O'Neill has apologised for the headbutt on a horse which could see him punished by the Horseracing Regulatory Authority.
O'Neill plants a headbutt on City Affair
He will be asked to explain his actions by the HRA next week after the incident at Stratford was caught by TV cameras.
O'Neill said: "I would like to say to the public that I'm very sorry they had to see such a thing. I've never done it before and it will never happen again."
O'Neill lost his cool when City Affair unseated him before a race.
Having reviewed a video of the incident at Stratford involving the John O'Shea-trained gelding, the HRA disciplinary panel is set to hold an inquiry on 3 August.
O'Neill told the Racing Post how City Affair had proven difficult to control, even before it unseated him.
He said: "The horse had been very unruly leaving the parade ring.
"When we went to look at the last hurdle before hacking down to the two-mile start, he started reversing when we got to the hurdle and went under a railing which he lifted out of the ground.
"It took me five minutes to leave the railings and get him down to the start which I had to do as gently as I could.
"When I got to the start he headed straight for a car with me, stopped five feet from the car, whipped round and dropped me.
"I landed on my feet, but a bit awkwardly for my knee and I was a little bit angry then, but I've never done anything like this before and I'm glad to say the horse is okay after it and I have spoken to John O'Shea."