Fatialofa's Worcester club released a statement saying the former Hurricanes lock was still in the Intensive Care Unit at St Mary's Hospital in London but was in a stable condition following his operation on Tuesday (NZT).
"Warriors lock Michael Fatialofa is resting and recovering in St Mary's Hospital in Paddington having undergone surgery last night to relieve pressure on his spinal cord caused by swelling," the statement said.
"The operation was a success and Michael is stable, but he remains in a serious condition and is receiving on-going care.
"The process of recovery and observation of improvement will now begin. As always our thoughts and prayers are with Michael and his family who we will continue support however we can as part of the Warriors family.
"Michael and his family are sincerely grateful for the support shown by the rugby community."
Fatialofa was taken to hospital after suffering the injury late in Worcester's big loss to Saracens last weekend.
He had been on the field for less than a minute as a substitute when he injured his neck in a collision.
In an earlier update, Worcester said their club doctor Nick Tait had been "in daily contact with Michael's neurosurgeon", after the injury had left him with "reduced power and sensation in his arms and legs".
Fortunately, scans had shown there were no broken bones in Fatialofa's neck.
Fatialofa is playing his second season with Worcester after moving north from a New Zealand career that saw him play for Auckland, Southland and the Hurricanes.