After returning home to Wales, the Wales flanker has had his injury assessed and will miss the start of the new season.
Commenting on Warburton's injury, Cardiff Blues Head of Medical John Miles said: "Sam suffered a grade three tear to his left hamstring in the second Lions test against Australia on the 29th of June.
"He had a scan with specialists in London yesterday which has shown the injury is already healing. He therefore does not need surgery but will require a period of rehabilitation between 12 to 16 weeks from the date of the injury.
"His rehabilitation will focus on range of motion, flexibility and specific strengthening of the hamstring in order for him to return to full health."
While Warburton's loss is a blow to the Blues and Director of Rugby Phil Davies, the region do have the likes of Josh Navidi and Ellis Jenkins as more than adequate cover.