It's fair to say the 2017 summer transfer window threw up some massive deals and rumours. The biggest story was perhaps Neymar's £198 million move from Barcelona to Paris Saint-Germain. It was so huge that the French club are now being investigated by UEFA after triggering fears over Financial Fair Play, but it's unlikely they'll be punished anytime soon.The deal sent shockwaves through the market and then led to Barca signing Borussia Dortmund's 20-year-old forward Ousmane Dembele for just under £95 million.  Manchester United and Chelsea were not far behind these two clubs in summer spending, with United buying Romelu Lukaku for £75 million and Chelsea bringing in Alvaro Morata for £58 million. But it was the Blues who were also involved in one of the biggest non-deals of the off-season. After months of speculation, Diego Costa will remain at Stamford Bridge until at least January.The 28-year-old has made his intentions of leaving clear and has barely been in London over the summer after falling out with manager Antonio Conte. The Italian reportedly sent his striker a text message telling him he wasn't in the squad's plans for this season and Costa has since been searching for a new club.He has his heart set on a move back to Atletico Madrid, but there was no chance of a transfer back to Spain as Diego Simeone's team are serving a transfer ban until January 2018.Numerous loan deals were also rumoured, with Galatasaray and Everton apparently interested, but neither materialised.Costa has now been named in Chelsea's 25-man Premier League squad for this season and the club fully expects him to train as he's still under contract.It now appears things have got even worse for the Spaniard, as David Luiz becomes the latest teammate to mock him on social media. After the transfer window shut, Thibaut Courtois posted a picture of him and Costa on Twitter, captioned "Se Queda" (stays) with three laughing emojis. 

Gerard Pique captioned a picture of him and Neymar with the same words on Twitter earlier this summer, before the Brazilian moved to France. 

Mocking both Pique and Costa, Luiz re-posted a picture of Chelsea legend Didier Drogba back at Stamford Bridge and used the same caption Courtois and Pique had. 

With posts like these, it's easy to see why Luiz is known as one of the biggest joker's in the Chelsea dressing room, even if he's poking fun at their wantaway striker.