There was a time during that period when the 21-year-old was deemed surplus to requirements by newly-appointed head coach Enzo Maresca.
Casadei did not play a single minute of pre-season and appeared highly likely to move to another club, either on loan or a permanent basis.
However, the Italy Under-21 international remained in West London past the end of August before being reintegrated back into the senior ranks by his compatriot.
Last week, Casadei was provided with his first start for Chelsea, completing the 90 minutes in a 5-0 victory over Barrow in the EFL Cup.
Maresca has since acknowledged that he plans to use the former Inter Milan starlet in a more defensive-minded role than he has been accustomed to in the past.
Casadei reveals summer talks
In over two years spent at Chelsea, Casadei has only accumulated 71 minutes - spread across 11 substitute outings - of Premier League football.
Nevertheless, speaking ahead of Thursday's Europa Conference League encounter versus Gent, he has given an insight of how he came to stay with the club for the rest of the year at the very least.
Casadei told reporters, as quoted by The Standard: "From the moment I decided to stay here, my goal is to become a Chelsea player — an important player for this team.
"It was my decision [not to leave on loan this season]. Last season was not very easy for me, so at the start of this season I was thinking about what was the best solution for me.
"From the moment I spoke to the manager, I was 100% sure that the decision to stay was best for me to improve and for my career."
He added: "I have always wanted to play for Chelsea. We are one of the biggest teams in the world so I could not be more proud to play for Chelsea."
Where does Casadei sit in pecking order?
Moises Caicedo, Romeo Lavia and Enzo Fernandez are regarded as the standout trio in the Chelsea engine room.
Kiernan Dewsbury-Hall - a former Leicester City player, like Casadei - is believed to be fourth in line, while the versatile Renato Veiga can also play as a defensive midfielder.
That effectively leaves Casadei as sixth choice, yet Maresca's comments on Wednesday seem to suggest that he can expect regular appearances in the Europa Conference League and EFL Cup.