Rangers got their first win at Celtic Park since 2010, closing the gap on the leaders to two points with a game in hand. Colombian striker Morelos was sent off in stoppage time after receiving a second booking for a dive in the box.
Morelos appeared to make a gesture with his hand across his neck to Celtic fans following his dismissal.
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"We believe Alfredo was racially abused and we would expect now that all measures will be taken to identify and deal with those responsible," a Rangers spokesman told Sky Sports.
Celtic said in a statement that they had not received any reports that the 23-year-old was racially abused.
"We are aware of the gestures made by the player towards Celtic supporters," Celtic said. "We have received no reports of any racial abuse but would fully investigate any should these be brought to our attention."