European Professional Club Rugby is also probing allegations that Delon Armitage, the Top 14 team’s full-back, directed offensive language at spectators at Welford Road.
Both incidents are being examined after complaints were made by Leicester, who toppled the reigning European champions 25-21.
Castrogiovanni sought out journalists after the match and unleashed a foul-mouthed assault on Leicester director of rugby Richard Cockerill, who had claimed the former Italy prop swapped the Tigers for Toulon in 2013 for financial reasons.
“I thought f*****g Leicester were f*****g amateur. I never want to speak with Cockers any more. I just don’t like c***s,” said Castrogiovanni, who spent seven years at Welford Road.
Armitage, who has a chequered disciplinary history, is alleged to have verbally abused spectators as he departed the pitch for half-time.
“Our disciplinary officer is now investigating those incidents to determine, among other things, whether there are grounds to bring misconduct complaints against those involved,” a statement released by EPCR said.
“The disciplinary officer has requested information from Leicester and the two players and will also review all other available evidence before deciding what the next steps, if any, will be.
“Should the disciplinary officer decide that there are grounds to bring a misconduct complaint in respect of one or both of the incidents, the case or cases would be heard by an independent disciplinary rules.”
Both players are free to play in Saturday’s return Pool Three match when Leicester visit Toulon.
Castrogiovanni has already taken the first step towards repairing the damage caused by his outburst by making an official apology.
“I want to make amends for my profanity and apologise to everyone feeling offended by what I said,” Castrogiovanni said in a statement published in the Guardian.
“I’m sorry if my words have created misunderstandings. It also was not my intention to offend anyone, but only to point out my position after some statements.”
“I hate lies and hypocrisy. I have always been a loyal person and I have been loyal to all the people I worked with. I have always loved the Tigers.”