The Senegalese international is wanted by Frank Lampard to increase competition with club-record £71m signing Kepa Arrizabalaga.
The Spanish international was also dropped last season after errors in games.
That included the FA Cup final, where Kepa was replaced by second-choice goalkeeper Willy Caballero, who is 38.
Following the defeat at home to Liverpool, Lampard said Caballero would start the Carabao Cup tie against Barnsley at Stamford Bridge on Wednesday.
He added: “Kepa has to keep working and he has to have support around him, that’s very clear.
“Individually players need support, particularly from myself, and I give that to all the players. And now we’ve got to try to give him confidence because that’s important.”