Sunderland have confirmed that they are investigating reports that a bottle was thrown at a Sheffield United player when the sides clashed last Saturday.
The club are currently reviewing CCTV footage after the incident allegedly took place at the Stadium of Light last weekend.
Match referee Jeremy Simpson, who handed a plastic bottle to the fourth official, is expected to include the incident in the report he will send to the Football Association.
Sunderland were 2-0 down after Clayton Donaldson, who signed for Sheffield United on deadline day, put the Blades in control.
Jack Rodwell netted to reduce the deficit but Simon Grayson's side now sit 20th in the Championship after three successive league defeats.
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