If they reach an agreement, Chelsea will look to revive Conor Gallagher's sale to Atletico Madrid.
Felix spent the second half of the 2022-23 campaign on loan at Stamford Bridge and scored four goals in 20 appearances for the Blues.
The 24-year-old Portugal forward played for Barcelona last season following another loan move but he has since returned to Atletico.
Gallagher, also 24, had been on the verge of joining Atletico this summer and even travelled to Madrid, but complications surrounding Samu Omorodion's proposed transfer to Chelsea saw the deal stall at the last minute.
Chelsea are interested in re-signing Atletico Madrid's Joao Felix, who spent half of the 2022-23 season on loan at Stamford Bridge
Felix, 24, was loaned out to Barcelona last season but he has since returned to Atletico Madrid
As a result, the English midfielder found himself on a flight back to London with his future unclear.
'He is doing some medical tests and some training.
'He won't be involved in the game. At this moment, he is trying to find a solution with the club.'
Meanwhile, Chelsea defender Bashir Humphreys is set to have a medical at Burnley on Monday ahead of a move to Turf Moor on a season-long loan.