The Football Association are seeking an explanation from Hull City after an object was thrown from the KC Stadium crowd on Saturday.
The incident in question occurred during the Tigers' 4-1 defeat to Sunderland and involved Black Cats defender Phil Bardsley.
The full-back saw a plastic bottle thrown in his direction shortly after he was on the receiving end of a tackle from Sam Ricketts which saw the Hull man shown a second yellow card.
Match referee Mike Riley recorded the matter in his match report and the FA are now obliged to investigate.
"We are writing to Hull for their observations of the incident and what steps are being taken to identify the individual responsible," said an FA spokesperson.
Meanwhile, Michael Turner is backing the Tigers to bounce back from their weekend disappointment when they face Manchester City on Boxing Day.
"We'll work hard as we always do when we've had a set-back," the centre-half told the club's official website.
"We lost 5-0 to Wigan here and we bounced back very well from that. We'll work hard and get ready for Manchester City."