The Wallabies playmaker has been ruled out of tomorrow's clash after suffering a setback in the days after his match-winning role against the Rebels in Melbourne.
Foley made a series of fearless, body-on-the-line tackles in his comeback game, but defended his and the Waratahs' medical team's decision to allow him to play.
"It's been a frustrating week, in terms of symptoms just re-occurring [but] nothing to do with the game last week," said Foley.
"It's just sort of come back after the game."
Foley, who is investigating osteopathy and vestibular rehabilitation therapy to speed up his recovery, said it was unknown when he would make another return.
The 27-year-old was initially sidelined for five weeks after copping a head knock in a pre-season trial against the Highlanders last month.
"It's a tough one. Ultimately, I think it is just time," Foley said.
"With the nature of head knocks and concussion, no one really knows.
"It is just time and you know when you feel right, when you're back to normal.
"When it first happened, you think you probably play the next week and it just sort of lingers and you just don't feel 100 per cent for a couple of weeks and it's still ongoing for me."
Despite the uncertainty, Foley said he was "not really worried" about his long-term health.
Coach Daryl Gibson admits it's a concern Foley felt fine to play against the Rebels, only to suffer another setback.
"The No1 thing is Bernard's welfare and we certainly don't want to put a player out there who's not ready," Gibson said.
Waratahs v Crusaders
6.05pm tomorrow
Crusaders: David Havili, Digby Ioane, Tim Bateman, Ryan Crotty, George Bridge, Mitchell Hunt, Mitchell Drummond, Whetu Douglas, Matt Todd, Jordan Taufua, Sam Whitelock (c), Scott Barrett, Owen Franks, Codie Taylor, Joe Moody.
Reserves: Ben Funnell, Wyatt Crockett, Michael Alaalatoa, Luke Romano, Pete Samu, Bryn Hall, Marty McKenzie, Manasa Mataele.
