The Belgian was absent from Chelsea's Cobham training ground without leave for the second time in two days on Tuesday, having been expected back for pre-season on Monday.
According to the 'Daily Mail', Courtois is now facing being fined £200,000, equivalent to two weeks' wages.
Chelsea have begun disciplinary proceedings against Courtois, who is seemingly attempting to force Chelsea into allowing him to move to Real Madrid this summer.
Courtois is keen on a move to the Spanish capital to be closer to his children, who live there with the player's former girlfriend.
The 'Blues' are in something of a catch 22 over Courtois as whilst they are currently demanding £45m for his services, the player is out of contract at the end of the season, meaning he could wind up leaving for nothing.
Courtois knows Madrid well having spent three years on loan with Atletico Madrid earlier in his career before returning to Stamford Bridge to claim the number one spot from Petr Cech.