"Specialists advised today that Jonah will be out of action for about six weeks", says Lomu's manager and wife, Fiona Lomu. "He hopes to begin light training again after that."
Lomu will be unavailable for the remainder of the Blues season, but expects to pull his boots on again for the NPC season with the North Harbour side.
"Obviously Jonah is very disappointed. He has worked so hard to get his fitness and his game back during his time in Wales - this is a set back for him but injuries like this happen all the time in rugby. Other than the ankle he's in excellent health and will be focused on getting right and preparing himself for the NPC season," said Fiona Lomu, his wife and manager.
Robert Norster, Cardiff Blues Chief Executive said: "Since his arrival in mid November, we have all been hugely impressedwith the sheer determination Jonah has shown to get back to playing top level rugby.
"His injury against Border Reivers was a cruel blow, especially given he was playing so well in what was his tenth game for the Blues this season. It was evident on Saturday how much progress Jonah hascontinued to make over the past six months and it's sad that he will not play again this season for Blues.
"He will remain with us until the end of the season and I'm sure I speak on behalf of everyone involved with the Blues, and indeed Wales, in thanking him for his significant contribution to date."