However the Wales international’s injury is not expected to rule him out of the tour to New Zealand, for which Warren Gatland will name the squad on April 17.
Warburton hobbled off during Cardiff Blues’ 24-24 draw with Ulster on Friday but scans have revealed that the injury was more minor than might have been feared.
"Sam has a low grade medial strain which will put him out for approximately six weeks, which won't interfere with the Lions," said Blues coach Danny Wilson.
"You see players who get back quickly if they follow religiously the protocol and they get a bit of luck.
"And I am sure that will be the case with Sam in terms of him following the protocol, and then we will see, all being well, how quickly he can come back. 'Low grade' was the important bit of news."
A period of rest could in fact be of benefit to the 28-year-old Warburton, who led the Lions on their victorious tour of Australia in 2013.
The Lions’ first Test against New Zealand will take place on June 24 at Eden Park in Auckland.