Manchester City opened formal club-to-club talks with Chelsea on Monday, and the two sides have since agreed a fee reported in the region of £137m, which would make Fernandez the most expensive signing in Manchester City's history and a contender for the most expensive in Premier League history.
He is waiting for the final go-ahead to travel for a medical, with the move still needing to be completed before Tuesday's 11pm deadline.
The Argentina international has been chasing the move for weeks, with personal terms understood to have been agreed with City some time ago, but the deal has stalled repeatedly over the size of the fee Chelsea have been demanding. Sources close to the west London club have indicated Chelsea grew frustrated with the pace of talks in the deal's final days, privately making clear to both Fernandez and City that they had no intention of letting the transfer run to the very last minute of the window without a resolution.
Fernandez is set to reunite with Enzo Maresca, who managed him during a productive spell at Chelsea before leaving to take over at City in the summer. Reports from France and Argentina claim the two clubs have now reached full agreement, though Chelsea are understood to have already done extensive work on potential replacements in central midfield, including Lamine Camara and Manu Koné, in case the move goes through.
Asked directly on Sunday whether Fernandez had played his final game for Chelsea, manager Xabi Alonso declined to give a clear answer.
"We'll see," he said. "We want the best for the team and that's why we made the decision against Luton and today, and anything that happens before Tuesday evening, we need to be aware of what is going to develop.
"We are not sure, we are preparing for all the scenarios, but I am sure that whatever happens from Wednesday we will have a good enough squad to compete in all the Premier League games."
Fernandez was left out of Chelsea's squad entirely for Sunday's match, having previously appeared only as a substitute in the club's opening-day win over Fulham, where he was jeered by sections of the home support.
Signed from Benfica for a then British-record fee in January 2023, he has gone on to make 170 appearances for Chelsea across all competitions, scoring 31 goals and providing 30 assists, and remains a World Cup winner with Argentina from that same year.