A mystery, unusual condition is the reason for Adam Ashley-Cooper's absence against the Reds for the Waratahs this weekend.
The Australia star is suffering from a condition called Baker's cyst – a swelling of the muscle behind the knee, with Ashley-Cooper looking to rest the unusual injury, rather than require surgery, after the cyst exploded.
The Waratahs medical staff are now consulting other professionals around the world before making a decision on how to treat the condition the right way.
"It's really unknown at the moment. If we really pushed Adam, he could have played. But we are treating it very cautiously for an injury where there is not a lot of information around," Waratahs assistant coach Daryl Gibson told the Sydney Morning Herald.
"We don't know what the prognosis is… is he going to come good in one week or maybe four weeks? We really want to tread carefully there.
"It started as Baker's cyst and then [after bursting] it has developed into something that has got the medical people a bit stumped.
"We are going to try to rehab that injury. There is not a lot of information about how we go forward.
"We are trying to take his scans to as many people and get a wide opinion. A lot of people haven't seen it before. That's why it is stumping a lot of people."
Matt Carraro has replaced Ashley-Cooper in the 13 jersey for Saturday's game with the Reds, with Peter Betham starting on the right wing and Wycliff Palu returning at number eight.