Greens MP John Kaye has been diagnosed with cancer and will not return when NSW parliament resumes at the end of February.
The Greens NSW have released saying Dr Kaye "will be unavailable for his Parliamentary duties prior to 30 March".
"Greens MP John Kaye has been diagnosed with cancer that has resulted in the need for therapy and treatment, including a hip replacement," the statement said.
"John has expressed his thanks for the strong support he has received from his family and his close friends at this time."
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The statement said Dr Kaye's spokesman duties of energy, education, treasury, finance, water utilities, consumer affairs, gambling and donations would be temporarily distributed among his Greens colleagues in NSW parliament.
"The Greens NSW wish John the very best as he confronts this health challenge," the statement said.
Dr Kaye was elected to the NSW upper house in March, 2007.
Prior to that he was an electrical engineering teacher and researcher at the University of NSW, where he specialised in sustainable energy and greenhouse issues.
He has also achieved a PhD University of California Berkeley and has worked as a volunteer, parliamentary policy advisor and campaign coordinator.
His colleagues and other community members have expressed their support for Dr Kaye's recovery on social media.