I pray in a mosque, but I do not believe that the leader of the prayers is a just man. However, if I leave…

I pray in a mosque, but I do not believe that the leader of the prayers is a just man. However, if I leave the congregation prayer, the people who pray there will notice that. This might be bad for the leader and make the praying people separate into two parts. My question is: Is it permissible to pray behind him without the intention of a congregational prayer?