Luke Nolen was to undergo surgery on Thursday to stem internal bleeding after a fall at trackwork at Pakenham.

The rider most famous for his association with champion mare Black Caviar was taken to the Alfred hospital after a fall with fractured left ribs and pelvis problems an initial concern.

But Victorian Jockeys Association Matthew Hyland on Thursday afternoon revealed that the full extent of his injuries had yet to be determined.

"Luke Nolen will undergo surgery this afternoon to stem the internal bleeding," Hyland said in a statement.

The injuries will extend a stint on the sidelines for Nolen, who has not ridden since the Sandown meeting on January 17 but was slated to make his return at Pakenham on Thursday night.