Blake Shinn is in doubt for the ride on No Looking Back in the Magic Millions Guineas on Saturday after being stood down at Gosford.

Shinn won Thursday's Listed Belle Of The Turf Stakes (1600m) on Cathay Lady but fainted in the stewards' room shortly after the event.

Shinn was attended to by ambulance staff and replaced on his remaining rides, including Testarhythm who went on to win the Listed Takeover Target Stakes with Brenton Avdulla aboard.

Racing NSW deputy chief steward Greg Rudolph says Shinn has to undergo a medical assessment on Friday.

The jockey has already been stood down from his rides at Canterbury on Friday night pending that assessment.

"He's stood down from tomorrow night pending a medical assessment. We'll be progressing with that tomorrow," Rudolph said.

"We'll determine his engagements for Saturday but it's doubtful he'll be riding Saturday and Queensland stewards will be advised this evening."

Shinn is due to ride the Gai Waterhouse-trained No Looking Back who is equal second favourite for the $1 million Magic Millions Guineas (1400m).

The jockey is hoping he will able to fulfil his engagements.

"I'll do everything I can to be able to ride the mounts," Shinn said before leaving Gosford.