Courtois, now 22, joined the Blues from Genk back in 2011, but was loaned out immediately to Atletico Madrid. The Belgian shot stopper ended up spending three years in the Spanish capital as Diego Simeone's side continued to renegotiate a loan deal for him.
Last season was his most successful to date, as Atletico won La Liga for the first time in nearly 20 years, whilst they also reached the Champions League final only to lose to city rivals Real Madrid. Atletico were keen on keeping Courtois either permanently or on loan for another season, but Chelsea boss Jose Mourinho wanted him back in West London ahead of the new season.
Now set to compete with long-term first choice Petr Cech this season, Courtois has a battle on his hands if he's to get in the first team on a regular basis - and his national team manager Marc Wilmots has warned him that he could be dropped if he doesn't play.
"Courtois will remain my No 1," said Wilmots. "But I know he could end up on the bench at Chelsea. In that case I will re-assess."
The situation has been made even more complex after Mourinho's latest comments. Courtois started in the friendly against Real Sociedad on Tuesday, but Mourinho says that it doesn't mean he will start against Burnley in Chelsea's Premier League opener on Monday.
"The fact he played (against Sociedad) does not say that he is my first choice for Monday against Burnley," said Mourinho.
The news will serve as a boost to Liverpool's Simon Mignolet, who starts every game for Liverpool and is the current understudy to Courtois at international level.