Sydney's premier apprentice Winona Costin has undergone surgery on a leg wound suffered in a trackwork fall.

Costin will be monitored in hospital for at least the next two days after cutting her thigh in the fall on Thursday morning.

Racing NSW doctor David Duckworth said Costin underwent surgery on Monday night.

"We had to wash out her wound and then close it," Duckworth said.

"She has to stay on a drip with antibiotics for 48 hours to prevent infection. Hopefully she will be discharged on Thursday."

Costin's hopes of defending the apprentices' premiership have been thwarted this season by injury with Rory Hutchings leading her by 29 to 16.

Koby Jennings joined Costin in second place on 16 with his four winners at Rosehill on Saturday including Ravi who was originally to be ridden by Costin.

Fellow apprentice Samantha Clenton was released from hospital on Monday, two weeks after she was injured in a multiple-horse fall at Taree.

Clenton suffered a broken collar bone and bruising to her back and is expected to be sidelined for another eight weeks.

Jackson Murphy, who was also involved in the Taree fall, will be out for six to eight weeks after damaging his spleen and suffering bruising to a lung.