Captain Kieran Read, Jerome Kaino and Dane Coles head a list of senior players already in a race against time to be match fit before the British and Irish Lions arrive next month.
Double World Cup-winning centre Williams left the field for a head injury assessment just before halftime and never returned.
Coach Tana Umaga told the New Zealand Herald he could not confirm the result of the assessment, but Williams displayed concussion “symptoms”.
Williams was injured when teammate and prop Pauliasi Manu landed on him, and Umaga said the team doctor advised he was not fit to return to the game.
“It will be a wait and see how he responds,” Umaga said. “It’s just how he pulls up today, how he pulls up tomorrow. He was still having symptoms after the game.
“What’s happened with concussion in the past... sometimes people respond well and can play next week, and sometimes they don’t.”
Williams’ injury comes as Charlie Ngatai returned to the Chiefs after a year sidelined by concussion. He scored a crucial try in the Chiefs win over the Reds to join a logjam of fit centres with Test experience.
Also vying for a midfield slot against the Lions are Ryan Crotty, Malakai Fekitoa, Anton Leinert-Brown, George Moala and Seta Tamanivalu.