Jockey Michael Walker has been taken to hospital after aggravating a back injury at Mornington.
Walker rode Duck Dynasty into third place in the second race before being taken off his only other scheduled ride at Monday’s meeting.
He was also stood down with the back injury at the Moonee Valley meeting on Saturday but gained a medical clearance to ride at Mornington.
“He was in quite a deal of pain,” Racing Victoria steward Rob Montgomery said.
“He hurt his back on Saturday and he’s been taken to hospital for assessment.
“We won’t let him ride again until he’s been assessed by our doctor Gary Zimmerman.”
Walker leads the Victorian jockeys’ premiership with 127 winners for the season, two clear of Dean Yendall, and has 33 metropolitan winners, putting him fifth in the Melbourne championship.