Scans revealed the 48-year-old fractured the T7 vertebrae in the middle of his spine when he slipped on wet stairs while getting ready for work on Tuesday morning.

Associate Professor Steve McGloughlin, the head of the intensive care unit at The Alfred hospital where Mr Andrews is currently a patient, said the premier was "comfortable and his pain is well-controlled".

"A multidisciplinary team including intensive care, trauma and orthopaedic specialists has developed a treatment plan, together with the Andrews family," Prof McGloughlin said late on Wednesday.

"Mr Andrews has sustained some serious injuries, and his condition is being monitored closely. At this stage there is no immediate plan for surgery."

A spokeswoman for the premier said: "On the advice of clinicians at The Alfred, there are no immediate plans for surgery".

There were concerns earlier on Wednesday that the premier would require immediate surgery on his spine, which would involve inserting screws or pins.

A months-long recuperation period would likely follow after such a procedure.

A government source told AAP there remains a "50-50 chance" Mr Andrews will still require surgery.

Doctors are expected to make an assessment later in the week, they added.

Mr Andrews also broke several ribs in the fall at a holiday home in the Mornington Peninsula but was cleared of any internal injuries such as a punctured lung.

He was initially treated at Peninsula Private Hospital but transferred to Alfred Trauma Centre in Melbourne after specialists assessed an MRI scan.

"Heartfelt thanks to the entire team at @AlfredHealth for taking such good care of me. We're so very grateful," Mr Andrews tweeted on Wednesday.

Deputy Premier James Merlino will serve as acting premier in Mr Andrews' absence.

Environment Minister Lily D'Ambrosio praised Mr Merlino, who is also the Minister for Education and Mental Health, at a press conference on Wednesday.

"James Merlino is a consummate politician and he's doing a fantastic job as acting premier," she said.

Ms D'Ambrosio said the premier was in "good spirits".

"He is in the very best of hands and I certainly wish him a speedy and full recovery so we can have him back on board as soon as possible."

Opposition leader Michael O'Brien said he had texted Mr Andrews and wished him well for his recovery.

"You put politics aside for a time like this. You don't like to see anybody going through that sort of pain, so I do genuinely wish him well," he said.

Australian Associated Press