Fernandez has been named on the substitutes' bench for Chelsea's clash with Sociedad in what is a shock move from Alonso following the midfielder’s transfer links.
The Argentina star has been close to a switch to Manchester City over the past week, with the Blues handing their Premier League rivals a 5pm deadline on Friday that City decided not to abide by.
As Alonso prepares for his first clash at Stamford Bridge, Fernandez may feature off the bench in what might be a mixed reception from the home crowd who are treated to a debut from Morgan Rogers.
Chelsea signed Rogers from Aston Villa in an incredible £117M move last month, making him Chelsea's record signing and, at the time, the most expensive British footballer ever.
He starts alongside Moises Caicedo and Cole Palmer who return to the side just under a week for the club’s opening Premier League clash with Fulham a week on Monday.
Maxence Lacroix also makes his debut after joining the club from Crystal Palace last month for around £52M, signing until 2032. He starts alongside Levi Colwill, captain Reece James, Wesley Fofana and fellow new signing Marco Palestra.
Chelsea XI: Sanchez; Fofana, Lacroix, Colwill; Palestra, James, Caicedo, Neto; Palmer, Rogers; Pedro
Subs: Penders, Slonina, Acheampong, Chavarria, Gusto, Hato, Essugo, Lavia, Barco, Fernandez, Estevao, Gittens, Quenda