Burnley say they have been informed about “offensive footage” on social media from some of their travelling supporters on Saturday afternoon.
The match was briefly halted after Williams drew attention to alleged racist sounds coming from the Estadio Civitas Metropolitano crowd.
Things have gone off the boil for Ten Hag at Old Trafford.
Chelsea thought they had overturned a 2-0 half-time deficit when Axel Disasi headed home, only for it to be ruled out for a foul on Diego Carlos.