Rangers said on Monday Colombia striker Alfredo Morelos was racially abused by Celtic fans during last weekend's Old Firm derby.
Morelos, 23, was sent off in the closing stages of Rangers' 2-1 win on Sunday following a second bookable offence and his side claim it was at that point he was targeted by home supporters at Celtic Park.
"We believe Alfredo was racially abused and we would expect now that all measures will be taken to identify and deal with those responsible," said a Rangers spokesman.
Celtic replied via a statement, saying: "We are aware of the gestures made by the player towards Celtic supporters.
"We have received no reports of any racial abuse but would fully investigate any should these be brought to our attention."
Meanwhile Morelos himself made what some viewed as inflammatory gestures by moving his hand across his throat as he made his way off the field.
Morelos's red card was his seventh in two seasons, with the forward still yet to score in an Old Firm game.
Rangers' first win at the home of their arch Glasgow rivals in nine years left them two points behind league leaders Celtic, who are bidding to win a ninth successive Scottish Premiership title.
