The Blues have already spent big to bring Mykhailo Mudryk to Stamford Bridge, while Noni Madueke, Joao Felix and Benoit Badiashile are among their other recruits.
Fernandez could follow from Benfica on what promises to be a busy deadline day as clubs across Europe scramble to get late deals done.
It remains to be seen if Arsenal can tempt Brighton and Hove Albion to part with Moises Caicedo.
Joao Cancelo looks set to swap Manchester City for Bayern Munich on loan and Paris Saint-Germain could finally seal a deal for long-time target Milan Skriniar along with Hakim Ziyech.
Stats Perform has picked out the standout transfers that could go through before the deadline.
BLUES TO SHOW THE COLOUR OF THEIR MONEY FOR WORLD-CUP WINNER?
Fernandez emerged as a target for Chelsea after his influential displays for Argentina during its World Cup triumph in Qatar.
The London club has wasted no time in building a new-look squad since a Todd Boehly-led consortium completed a takeover and Graham Potter arrived as manager.
Chelsea has already made huge statements this month, none more so than snaring winger Mudryk from under the nose of Premier League leader Arsenal.
Chelsea is working on trying to secure the services of Fernandez for a reported fee of £105.5million (€120m), which would break the Premier League record of £100m City paid Aston Villa for Jack Grealish.
CAICEDO A NO-GO?
Arsenal has already raided Brighton to bring want-away winger Leonadro Trossard to the capital.
The Gunners have failed with big-money offers for centre midfielder Caicedo, who last week made it clear he wants to join the Premier League leader.
Arsenal is said to be ready to test the Seagulls' resolve again on deadline-day with a third bid of £75m, but Brighton wants to keep him for the rest of the season.
If Brighton does not get an offer it cannot refuse, Arsenal could turn to Leicester City's Youri Tielemans or Chelsea's Jorginho.
Eyebrows were raised when it came to light that Bayern is poised to bring Cancelo to the Bundesliga from Manchester City.
The Portugal full-back Cancelo has fallen out of favour at the Etihad Stadium, having reportedly had a bust-up with Pep Guardiola.
A loan deal would be great business for Bayern as it hunts more trophies and this one is expected to go through.
PSG'S SKRINIAR PERSISTENCE COULD PAY OFF, ZIYECH TO FOLLOW?
While Bayern's move for Cancelo has come late in the window, Skriniar has long been a target for PSG.
The Inter centre-back is only under contract at the end of the season and with the Serie A giant unable to tie him to a deal, it has been seemingly only a matter of time before he moves on.
PSG should finally get its man before the window closes, with the defender having already confirmed he has agreed terms with the Ligue 1 champion. Chelsea winger Ziyech could also be on his way to the French capital.