Ex-Hockeyroo admits she pretended to have cancer, and faked medical letters.

A former Hockeyroo who claimed to be terminally ill with cancer has admitted faking a doctor’s certificate and medical letters to cheat a cancer charity out of tens of thousands of dollars.

Kathryn Hubble told workmates at cancer charity Redkite she didn’t “have a great deal of time” but her story unravelled after the charity hired an investigator to look into the forged letters.

Redkite, a registered charity supporting children and adults with cancer, estimates Hubble cost them more than $47,000, court documents show.

The 32-year-old is expected to be sentenced in Sydney’s Downing Centre Local Court next week after pleading guilty to making and using false documents for a financial advantage.

Hubble faked a medical certificate and letters for unentitled sick pay and told a co-worker “my cancer is serious … it is terminal”, according to a statement of facts.

“I don’t have a great deal of time,” the ex-goalkeeper said.

The facts reveal Hubble first advised Redkite she had health issues and provided two medical letters from an oncologist in 2014 when she worked for the registered charity in Western Australia.

She later requested and was granted a transfer to Redkite’s Sydney office for cancer treatment – with the charity creating a position to accommodate her.

It’s estimated to have cost Redkite $47,855, including $35,488 in wages and costs of $12,407, as the West Australian position had to be filled after her transfer.

This year the charity requested documentation from her treating doctors and received an email and attached medical certificate purportedly from a doctor at North Shore Private Hospital.

“I have seen her today and am happy with her progress and for her to be working in the office environment with the flexibility you have been providing thus far,” the email said.

The doctor later told police he had no record of seeing Hubble or issuing a medical certificate.

Hubble subsequently sent from her own email address two letters purported to be from another doctor at Darlinghurst Medical Centre.

The first letter gave advice on what to do if she fainted at work. The next letter said Hubble was beginning six months of immunotherapy treatment and would either need to work from home or have separate bathroom facilities for 48 hours after each treatment.

The doctor later told police the letters were not prepared by him but did carry his correct signature.

During a police interview in August she admitted the medical certificate and letters were fake.

Redkite on Tuesday said they sacked Hubble earlier this year and "provided every assistance" to the police investigation.

"Redkite acted immediately upon becoming aware of possible misconduct and referred the incident for investigation to the NSW Police," a spokeswoman said in a statement.

"Our focus, as always, remains with the continual delivery of our essential support to children and young people with cancer and their families."

Hubble was a back-up goalkeeper in a handful of Australian hockey squads in 2010-11, but was never selected in an Olympic or Commonwealth Games team.