Mauricio Pochettino admits midfield duo Enzo Fernandez and Moises Caicedo need to improve after Chelsea's poor start to the Premier League campaign.
The Blues' midweek 2-1 defeat at Manchester United kept them in 10th place, five points behind West Ham in ninth.
And Pochettino believes big-money signings Fernandez and Caicedo need to up their levels but acknowledged the two 22-year-olds' development is a 'process'.
Speaking ahead of Chelsea's Premier League clash with Everton on Sunday, he said: 'The relationship between them needs to improve of course, between them and individually also.