A furious Mario Balotelli asked fans whether racism was "legal in France" after the Nice striker accused Bastia supporters of abusing him during his team's 1-1 Ligue 1 draw on Friday, prompting a French League investigation.
The Italian posted a message on his Instagram page on Saturday, saying the incident was a "real shame".
"Yesterday the result against Bastia was right... we will work more and try to get our objective... the referee was good, too, but I have a question for French people... Is it normal that Bastia supporters make monkey noise and 'uh-uh' for the whole game and no-one of the "commissions discipline" say nothing?," Balotelli, on loan from Liverpool this season, wrote.
"So is racism LEGAL in France? Or only in Bastia?
Football is an amazing sport ... those people like Bastia supporters make it horrible."
In a statement on their website, Nice gave their full support to Balotelli, adding that stones had been thrown at their team bus ahead of the game.
"We are ... shocked to learn of the behaviour towards our players, especially Balotelli. The club congratulates them for remaining calm and not reacting and give them their full support," Nice said in a statement on their website.
The French League (LFP) said it would investigate the incidents in its next disciplinary commission meeting on Thursday.
Later on Saturday, it added that it was sending footage from BeIN Sport TV channel, showing some Bastia fans racially abusing Balotelli, to its disciplinary commission.
Bastia were docked two points by the LFP in the 2007-8 season after fans racially abused a Libourne St Serin player during a Ligue 2 game.
"Having not been informed last night, by the referee, the delegates or any member of OGC Nice, that any incident had occurred, it is with amazement that we discover allegations damaging the image of Sporting (Bastia)," the club said in a statement sent to Reuters.
Bastia said it was for the LFP to shed light on the incidents.
Nice are top of the Ligue 1 standings with 46 points from 21 games. Bastia are 15th on 21 points.