Sonny Bill Williams has joined the All Blacks injury crisis list, with the Blues back's immediate future in doubt because of concussion.

Coach Tana Umaga has confirmed this morning that SBW was displaying concussion symptoms, although he was unable to confirm whether he had failed an official assessment during the Blues' win over the Waratahs in Sydney.

Umaga did not want to speculate, saying the Blues took concussion situations very seriously, and as recent events had shown, it was hard to know sometimes if players would be out long term.

Umaga said he had been advised by the Blues doctor that SBW was not fit to continue against the Waratahs.

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Williams left the field after team mate and prop Pauliasi Manu landed on him, and did not return for the second half.

"It will be a wait and see how he responds," said Umaga.

"It's just how he pulls up today, how he pulls up tomorrow. He was still having symptoms after the game.

"He just wasn't feeling well. What's happened with concussion in the past...sometimes people respond well and can play next week and sometimes they don't.

"We are seeing cases now where people don't come back. I don't want to put him in that box. He was up and about and alert but knew himself he was feeling off

"No one knows their body like themselves. we will take every precaution.

"I just talked to the doctor, who said I don't think he should go back on. I don't know if he failed the test as such."

The Blues play the Cheetahs on Friday.