The 33-year-old prop launched a scathing attack on the Premiership side and their coach Richard Cockerill following Toulon's 25-21 defeat to Leicester in the European Champions Cup on Sunday.
Castrogiovanni is reported to have taken exception to Cockerill's previous claim that he left for the Top 14 side in order to make more money.
European Professional Club Rugby (EPCR) - the governing body which controls the European Rugby Champions Cup and the European Rugby Challenge Cup - already announced that it will hold a review into the incident.
EPCR also confirmed it was looking into accusations that Castrogiovanni's team-mate Delon Armitage "used offensive language at or near spectators".
Toulon have now acknowledged EPCR's investigation and are set to hold an internal inquiry, stating that both players could face punishment.
"Toulon takes note of the decision of EPCR to open an investigation after Leicester decided to report the behaviour of Martin Castrogiovanni and Delon Armitage during and the match of Leicester and Toulon on Sunday," read a statement on Toulon's official website.
"Toulon decided to conduct [an] investigation internally and could punish players if it is deemed necessary."