Fikayo Tomori admits "nothing was explained to him" as he struggled to impress at Chelsea before eventually leaving for AC Milan.
The centre-half secured a January exit as his game time became increasingly scarce.
Tomori enjoyed a loan spell away from the Blues at Derby and excelled under Frank Lampard's guidance.
That helped him upon his return as Lampard was appointed Chelsea boss which meant the 23-year-old was given first team opportunities.
This season though, following the arrival of Thiago Silva, he found minutes hard to come by as the Brazilian formed a partnership with Kurt Zouma.
Despite being told to work hard in training in order to get his place back Tomori felt as his his efforts were not being rewarded.
“I was suddenly out of the squad and I don’t really know why,” Tomori explained to the Telegraph .
“I just thought I needed to work hard. Then I went to speak to the manager and he said you’ve just got to train harder, so I took that on the chin and thought that’s what I had to do.
“Mentally, it was difficult because you just want to be playing and on the pitch, and feel part of the team.
"And it was difficult for me because I wasn’t really feeling part of the team and I was wondering what had happened.
“I was trying to do extra and push myself more but, at that time, nothing seemed to work and nothing was explained to me.
“It was so frustrating. 2020, football-wise, was very, very difficult, especially after the way 2019 had gone for me playing games.
"From being at 100 to literally going down to zero and then not knowing the reason why it had gone to zero, it was very challenging.”
Tomori moved to the San Siro on loan but the Italian side have the option to make the move permanent at the end of the season.
