Thibaut Courtois has signed a new five-year contract with Chelsea, putting Petr Cech's future into further doubt.
Courtois has begun the Barclays Premier League season, his first with the Blues despite signing in July 2011, as first-choice goalkeeper ahead of Cech.
Now Cech, the Blues' number one for a decade, could be left to seek pastures new in January after Chelsea placed further confidence in Courtois by handing him a new deal.
The 22-year-old spent three seasons on loan at Atletico Madrid after joining the Blues from Genk in his native Belgium.
Courtois returned to Stamford Bridge this season and made his debut in a 3-1 win at Burnley as the first of three successive appearances under Jose Mourinho.
A statement on chelseafc.com read: "Chelsea Football Club is pleased to announce Thibaut Courtois has today signed a new five-year contract."
Courtois added: "I'm very happy with this new deal, it's really nice to have signed this new contract for five years.
"My future was already sorted but it's nice to know I'm going to be here for another five years and now I can just concentrate on playing games.
"I hope we can win a lot of games and trophies."
Courtois' return has placed Cech in an unfamiliar predicament, on the substitutes' bench.
It is a situation reminiscent of when Cech was installed as number one ahead of the established Carlo Cudicini after his signing from Rennes in June 2004. That was also a decision made by Mourinho.
The 32-year-old Czech Republic goalkeeper has two years remaining on a four-year contract he signed in 2012 after helping Chelsea to the 2012 European Cup.
Whether he now sees out the deal remains to be seen, with Paris St Germain and Real Madrid among the clubs who were reportedly monitoring his situation closely during the summer transfer window.
Despite being a newcomer to the Chelsea team, Courtois, who had two years remaining on his existing deal, has proved his credentials on the big stage.
He won Spain's Primera Division title with Atletico last season and the Europa League in 2012.
Three times he played against Chelsea for Atletico - in the European Super Cup in 2012 and in last season's two-legged Champions League semi-final, when he played at Stamford Bridge as a Blues player for the first time.
Atletico prevailed, but lost to city rivals Real Madrid in the final.
Courtois was also Belgium's first-choice goalkeeper at the 2014 World Cup finals in Brazil, when they reached the quarter-finals.