Chelsea have done some good business towards the end of the transfer window.Thibaut Courtois' desire to leave the club forced Chelsea to act fast, and they secured one of the best up-and-coming goalkeepers in world football to replace him in Kepa Arrizabalaga.They then managed to secure a loan deal for Mateo Kovacic from Real Madrid, with Courtois heading in the other direction.That bolsters Maurizio Sarri's midfield options significantly.Kovacic has shown his pedigree in the last few years, having performed at a high level with Inter Milan, Real Madrid and for Croatia.But one aspect of the deal could well be a huge mistake for Chelsea.It has been revealed that there is no option to take Kovacic on a permanent deal at the end of his loan.That could well be a big error on Chelsea's behalf. If Kovacic impresses, Real Madrid could decide against selling him to the west London club.But, it also has further implications, a point that Independent journalist Ed Malyon has picked up on.Malyon believes that the deal means Chelsea are now developing other teams players rather than their own.He wrote: "No permanent option in Kovacic deal, so Chelsea are just developing players for Real Madrid while Loftus-Cheek and co sit on the sidelines."

He's not wrong. Kovacic is likely to take game time away from encouraging youngsters such as Ruben Loftus-Cheek.

Although in the short term it could be beneficial for Chelsea, it could have a negative impact in the long term.

Kovacic could thrive and return to Real Madrid as a better player, while Loftus-Cheek could suffer with his first team opportunities limited.

Chelsea could well regret failing to include a permanent option on Kovacic' loan.

Meanwhile, Kovacic has stated he will give his all for Chelsea during his stint at the club.

"I am really happy and excited to be here at Chelsea," he told Chelseafc.com, per Sky Sports. "It is an amazing feeling. I will try to do my best for this club.

"It is a new league for me, the beginning is always tough but I am sure the coach and my new team-mates will help me and I am looking forward to a great season."