The Scotland centre suffered a triple fracture of the C1 vertebra during the second half of the pre-season fixture.
An MRI scan on the injury revealed surgery was not required and the 27-year-old has spent the last three months at his family home in Scotland wearing an external fixation device, which was removed last week to allow him to return to London and continue his recovery.
He said: "I would like to thank everyone, especially my family and friends, for their support.
"I have been inundated with messages from not only London Irish and Scotland supporters, but the wider rugby community too.
"Your support has really got me through this tough time in my life and I am very grateful for that. I am glad to be back at London Irish and looking forward to catching up with my team-mates."
Glasgow-born Ansbro has won 11 caps for Scotland after making his debut against South Africa in 2010, scoring three tries, including one against Romania in last year's World Cup.
He joined London Irish in the summer of 2011 after beginning his club career with Northampton.
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