Champion apprentice Jason Watson was taken to hospital after suffering a heavy fall at Kempton.
The talented rider was partnering the Jeremy Noseda-trained Teresita Alvarez at the Sunbury circuit when his mount clipped heels and stumbled badly in the very early stages of the one-mile contest.
Watson was thrown to the ground and had to be stretched off the course.
Barney Clifford, clerk of the course at Kempton, said: “He’s been taken to hospital at St George’s in Tooting for further assessment.
“He was fully conscious and I was talking to him myself.
“He was put on a body board as a precaution.
“That’s all I can tell you at the moment.”
Watson enjoyed a whirlwind campaign in 2018, hitting the headlines in the summer when winning the Stewards’ Cup at Goodwood for Hugo Palmer aboard Gifted Master.
The teenager also bagged Group One honours for the retiring Luca Cumani through God Given in Italy before being confirmed as number one rider to leading trainer Roger Charlton for the 2019 campaign.