The Inter Milan goalkeeper, who has 34 caps for the Indomitable Lions, started their 1-0 defeat to Switzerland in their opening World Cup game before clashing with head coach Rigobert Song over his playing style.
Onana preferred to play out from the back as evidenced by his 26 touches outside the box against the Swiss but Song wanted a less risky approach.
The 26-year-old played no part in Cameroon's thrilling 3-3 draw with Serbia on Monday after which it was announced that he had been dropped from the squad.
In a statement released on Twitter, Onana explained his version of events, which read: "Yesterday I was not allowed to be on the ground to help Cameroon, as I always do, to achieve the team's goals. l always behaved in a way to lead the team to success in a good manner.
"I have put all my efforts and energy into finding solutions to a situation that a footballer often experiences, but there has been no will on the other side. Some moments are difficult to assimilate.
"However, I always respect and support the decisions of the people in charge of pursuing the success of our team and country. l extend all my strength to my team-mates because we demonstrated that we are capable of going very far in this competition.
"The values that I promote as a person and as a player are the ones that identify me, and that my family has given me since my childhood. Representing Cameroon has always been a privilege. The nation first and forever."
Cameroon will need to win against Brazil in their final group game to stand any chance of advancing into the knockout rounds.
