Jockey Michael Walker has been stood down and taken to hospital after winning the Group Two Queensland Guineas aboard Sambro at Doomben.

Walker had to be assisted back to the jockeys room after being in a distressed state as Sambro was pulling up following his victory on Saturday.

He was replaced on his rides later in the day, including Foxplay in the Group One Stradbroke.

Chief steward Allan Reardon said he was waiting for a report on Walker from the hospital.

Credit: AAP