Costa has been hoping to join Atletico Madrid after being told by Chelsea boss Antonio Conte he was no longer wanted at Stamford Bridge.
But Atletico have been unable to agree on a fee with Chelsea.
And in a Twitter post similar to one by Gerard Pique about Neymar before he eventually joined Paris Saint Germain last month, Courtois wrote: “SE QUEDA” along with three laughing emojis and a picture of himself holding last season’s Premier League title with Costa.
The phrase translates to ‘he stays’ suggesting Costa will be at Chelsea next season and that Courtois is happy to still have the Spaniard around.
The post itself quickly reached 10,000 retweets with most fans delighted at the news.
Courtois’ post also follows Costa’s inclusion in Chelsea’s Premier League squad for the season.
Squad lists had to be submitted today, with the Premier League confirming the selections on their website.
More Breaking News:
Diego Costa: Chelsea striker left out of Blues’ Champions League squad – Duncan Castles
That’s according to respected transfer specialist Duncan Castles as speculation surrounding the Spain international’s future rumbles on.
Costa revealed in June that Antonio Conte had informed him by text that he was free to leave Stamford Bridge this summer.
And that led to widespread rumours that he could return to Atletico Madrid, where he made his name before joining Chelsea.
Costa confirmed that he wanted to re-sign for the La Liga giants and has spent the couple of months in Brazil waiting for a switch to materialise.
That situation angered Chelsea chiefs, who’ve failed to agree a fee for Costa to head back to Atletico.
And with the Spanish transfer window coming to a close on Friday night, it seems the 28-year-old will be forced to return to London.
Chelsea have dropped a big hint that Costa will be around for the coming season by including him in their Premier League squad.
However, it seems all is not well between player and club still, with Castles hearing Costa’s been omitted from Chelsea’s Champions League squad.
On Twitter, Castles wrote: “Am told that Diego Costa has been excluded from Chelsea’s Champions League squad.”
Chelsea return to Champions League group stage action in September and are due to face Atletico, Roma and Qarabag.
And Conte’s side look set to go into those ties without wantaway Costa among their ranks.