Monaco have pulled out of the deal to sell Lamine Camara to Chelsea, who feel the French club have acted in an extraordinary and deeply unprofessional way.
Camara was set to join Chelsea for £47m and sign a six-year deal pending a medical.
Just after the 11pm transfer deadline passed, news emerged that Monaco reneged on their agreement with Chelsea and informed the Blues of their decision in writing.
Monaco pulled out because they had successfully renegotiated the deal to sell Folarin Balogun to Everton,
Monaco only wanted to sell one player, and after agreeing to sell Balogun to Everton, they pulled out of the Camara-to-Chelsea deal despite a full written club-to-club agreement with the Blues.
Monaco refused to sign a Camara deal sheet before the 11pm deadline, so there was no chance of Chelsea resurrecting a deal for the Senegal international.
The feeling at Chelsea towards Monaco now is likely to be "what goes around comes around".
Chelsea had been looking for a new midfielder with
Chelsea had the option to pull the plug on Fernandez's move to Man City after the Camara deal collapsed, but they stuck to their word and honoured their commitment to complete the deal.
Roma's Manu Kone was also shortlisted as a potential option, while Chelsea were also looking at midfield options in the Premier League.
Your Site News' Kaveh Solhekol:
"Enzo Fernandez is going to be a Manchester City player. Lamine Camara to Chelsea collapsing is totally separate.
"Chelsea have not been able to sign a replacement. Chelsea are really unhappy with the way Monaco behaved.
"My information is everything was done - written, agreed, signed. He was flying into London [on Wednesday].
"At the same time, Monaco have been negotiating with Everton to sell Folarin Balogun. Once they agreed a deal with Everton, they came back to Chelsea and went back on their agreement.
"Chelsea don't believe this is the way clubs should conduct business. I suppose this is one of the risks you take when you leave things so late."
Chelsea goalkeeper Robert Sanchez has completed a season-long loan move to Serie A side Como.
The goalkeeper had been bumped down to Stamford Bridge following the arrival of Emi Martinez from Aston Villa.
Elsewhere, midfielder Dario Essugo has completed a season-long loan move to sister club Strasbourg. Essugo was of interest to Hull in this window.
Striker Deivid Washington has completed a permanent transfer to Strasbourg. He signed from Santos for £17.1m three years ago but made only three appearances.
Forward Dujuan Richards has also joined AFC Wimbledon on a season-long loan.
Meanwhile, Chelsea striker Shim Mheuka has arrived in Glasgow ahead of his loan move to Celtic, who are also working to finalise a deal for Chelsea left-back Landon Emenalo.
