England lost a thrilling 'Pool of Death' match 25-28 to leave them in danger of becoming the first World Cup hosts not to reach the knockout stages and that defeat could be compounded by any disciplinary action that may be taken against flank Wood.
Williams went off 14 minutes from time when he was struck on the head by Wood's shin as the back row forward attempted to hack a loose ball towards Wales' line.
After several minutes of treatment, Williams left the field on a medical cart and must now begin the "return to play protocols" governing concussion. These could see him ruled out of Wales' remaining pool matches against Fiji and Australia.
For injury-hit Wales, that would be yet another blow to their back division.
Wales had fullback Leigh Halfpenny and scrumhalf Rhys Webb ruled out before the World Cup started, while centre Cory Allen (hamstring) was sidelined after their opening 54-9 win over Uruguay.
Star centre Jonathan Davies had already been ruled out earlier this year after suffering a serious injury playing for his French club Clermont. And as well as losing Liam Williams, Wales also saw wing Hallam Amos (shoulder) and centre Scott Williams (knee) go off injured against England.
Wood took to social media to apologise to Williams but even if his action is not deemed deliberate, his action is ruled to be reckless.
World Rugby regulations state a citing complaint must be made within 36 hours of the match ending, which means that 10.00 local time (09.00 GMT) Monday is the deadline for disciplinary action to be taken against Wood.
In his Twitter message, Wood said: "@SanjayWills really relieved to hear ur back on ur feet ok mate.Horrible to see u stretchered off because of me.Hope u hav a speedy recovery [sic]."
Wales assistant coach Shaun Edwards said they had reviewed the incident and were considering whether to refer it to the citing commissioner.
"There was definitely contact between part of Tom Wood's body and Liam's head. It is something we are going to look at. I think we will make a comment on that later on. We did lose one of our best players," Edwards said.
