Canberra Racing chief executive Andrew Clark said Cahill was taken to hospital with neck pain, but was believed to be OK, while apprentice jockey Ellen Hennessy suffered dizziness following the fall.

Both were stood down for the rest of the race meet.

Cahill's absence opened the door for fellow jockey Robyn Freeman to guide the Norm Gardner-trained Cyborg to victory in the Federal (1400 metres) - which was originally Cahill's ride.

His fall occurred in the previous race - the maiden plate (1000m) won by Matthew Dale's Penthouse - when Cahill's mount Shafted Hero blundered on the back straight, leading to both jockeys coming off.

MORE CANBERRA SPORT

Shafted Hero was put down after the race.

"Unfortunately two riders came down. Mathew Cahill was transported to hospital - he should be OK," Clark said.

"Ellen Hennessy is OK as well.

"[Cahill had] neck pain, but he did have movement and was conscious. He's been transported to Woden hospital, whereas Ellen Hennessy was dizzy.

"They've both been stood down from both their rides for the remainder of the day.

"Mathew was due to ride that winner of the Federal.

"One horse was unharmed. One horse was euthanised."