British and Irish Lions captain Sam Warburton faces a race against time to be fit for Wales' autumn Test campaign after being ruled out for 12 to 16 weeks with a hamstring tear.
The Blues had feared Warburton would face a lengthy lay-off, and the club have confirmed he will not play until at least October.
Blues' medical chief 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 has 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."
Warburton, 24, will miss the Blues opening run of RaboDirect Pro12 fixtures and is unlikely to be involved in their opening two Heineken Cup pool fixtures.
The openside's absence is a major blow for the region as they look to rebuild after struggling last season.
But a four-month absence would effectively rule him out of head coach Warren Gatland's plans.