Mario Balotelli has been backed by teammate Alassane Plea, who said he heard Bastia supporters racially abusing the Nice striker during Friday night's 1-1 draw.
On Saturday, Balotelli described the abuse he heard at the Armand Cesari stadium and complained that the French league had not acted swiftly.
And on Sunday, Plea -- Balotelli's strike partner -- told French football show Telefoot he had heard the abuse.
"Yes, I can confirm it. We heard it during the warmup [and] during the game as well, monkey chants," he said.
"At the end of the game he [Balotelli] was very, very upset. They insulted him the whole game. It's dreadful to hear these things on a football pitch."
Broadcaster beIN SPORTS released footage showing a handful of Bastia fans in one section of the stadium racially abusing Balotelli.
It showed one man standing up and making loud monkey noises while Balotelli warmed up.
The French league (LFP) said on Saturday night that it had viewed this footage and opened an investigation.
Its disciplinary committee will meet on Thursday, with more information to come from officials and both clubs.
REAL SHAME. pic.twitter.com/dEzSRn87N1
- Mario Balotelli (@FinallyMario) January 21, 2017
Although Bastia said on Saturday they were not aware of any abuse taking place, they stressed they were at the LFP's disposal "so that all light is shed" on "this type of behaviour, which is by nature stupid and unacceptable."
Early on Saturday, Balotelli wrote about the abuse he suffered on his Instagram and Twitter pages.
"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 wrote, referring to the LFP's disciplinary committee.
"So is racism legal in France? Or only in Bastia? Football is an amazing sport. Those people like Bastia supporters make it horrible!"
Balotelli, 26, the son of Ghanaian immigrants to Italy, concluded his post by writing in French that what happened was "une vrai honte" -- a real disgrace.
He did not say in his message whether he had informed referee Clement Turpin -- who had the authority to stop the game -- of the crowd's actions.
Bastia were docked two points by the LFP in the 2007-08 season after fans racially abused Burkina Faso forward Boubacar Kebe by holding up a banner during a second division home game against Libourne.