Italian police and magistrates are examining photos and video to decide whether one of the country's best-known footballers gave a fascist salute.
Di Canio gave the straight arm salute after Thursday's derby
Paolo di Canio appeared to make the gesture after his team Lazio beat local rivals Roma 3-1.
Di Canio previously played for Celtic in Scotland and English teams West Ham, Sheffield Wednesday and Charlton, as well as Juventus and AC Milan in Italy.
It is not the first time the player, Lazio and the Rome derby have been the source of controversy.
Last season's match was abandoned when rival fans threatened to invade the pitch after unfounded rumours circulated that a young fan had been killed by a police vehicle.
While this season's game was less dramatic, it was sensitive nonetheless.
Di Canio, a Lazio fan all his life, had played well and scored a stunning goal.
On Saturday, though, Italian newspapers carried pictures of Di Canio's face distorted with pride.
His right arm was apparently raised in a straight-armed Roman salute that would have been instantly recognised by the former fascist leader of Italy, Benito Mussolini.
It would also have been recognised by the minority of far-right, racist supporters who have given Lazio a bad name over the years.
It has now been confirmed that police are sifting through photographs and film footage of the incident to see if Di Canio's actions merit any criminal charge.
Italy's football authorities are also expected to examine the evidence.
Lazio is the club forever associated with fascism. It was Mussolini's team and he was often seen in the stands.
Elsewhere in the world, "fascist" is a lazy catch-all political insult, but in Italy it still carries a much heavier and more specific charge.
As one charitable observer - the Telecommunications Minister, and Roma supporter, Maurizio Gasparri - put it, Di Canio's excitement clearly got the better of him.
"Poor lad," said the minister. "Like all Lazio supporters, he is just not used to winning."