WARATAHS star Bernard Foley is in doubt to play the Crusaders on Sunday after concussion symptoms returned after the Super Rugby win over the Rebels.
A Waratahs statement said the five-eighth was medically cleared to play against the Rebels and passed all return-to-play protocols for the game, but added that "symptoms that were gone have returned".
The Waratahs' medical team is now "undertaking additional treatments".
Foley suffered the head knock in the Waratahs' final pre-season game against the Highlanders and the round-five win over the Rebels was his first action of the season.
"Bernard's welfare is our priority right now and our medical team are taking an active treatment process to manage his symptoms," Waratahs coach Daryl Gibson said.
"We will follow the medical advice and he will undergo further testing and treatment prior to any decisions being made about him returning to playing."
Speaking before the Rebels game last week, Foley opened up about the extent of his concussion torment.
"It's quite a scary injury in that blokes can get knocked and not come back from it," the 27-year-old said.
"They can be innocuous or they can be the prone knockout.
"No one really knows about this issue.
"There's no deadline or guideline as to how long before you're going to be back."
Foley flew to South Africa for the Waratahs' two tour games but was forced to return home early to see a specialist as the symptoms continued.
The symptoms included headaches and being overly light sensitive, including reaction to TV, computers or mobile phones.
Some days he'd feel fine, others not.
"That was probably the frustrating thing, the things that were lingering," Foley said.
"Head injuries are something very serious and something very relevant at the moment, I suppose, with the way it's been handled in rugby league and rugby union.
"The player's welfare is paramount in terms of making sure people are safe and right in going back on (the field)."