Franks has been sidelined since doing damage during a Super Rugby victory over the Brumbies this month.
The Northampton Saints-bound All Black does not require surgery, but will not return until the start of June at the earliest.
"The good thing is it doesn't require surgery, so it will be a good rehab process," said Crusaders assistant coach Jason Ryan.
"It's obviously a relief for everyone. It was touch and go there for a bit. Get him back in a month, all going well.
