Kasabian say former frontman Tom Meighan misled fans by choosing not to talk about his domestic abuse charge.
Meighan admitted one count of assault by beating on 9 April at Leicester Magistrates' Court on Tuesday morning and was sentenced to 200 hours of unpaid work.
In a statement to fans, the band say they are "completely heartbroken" by the departure of Meighan, but added they were left with no choice but to ask him to leave.
"There is no way we can condone his assault conviction. Domestic violence and abuse of any kind is totally unacceptable," they said.
"As soon as we found out about the charges made against Tom, we as a band made the decision that we could no longer work with him.
"We were led to believe that Tom would hold his hands up and in his statement tell everyone what he'd done but he chose not to, misleading a lot of fans."
The band continued: "Ultimately, as much as Tom has hurt us all, we're not the victim in all of this. Domestic violence is something that can never be excused."
Kasabian said that they had waited to comment on the case until after it had finished in court.
In court he admitted pushing his ex-fiancee into a hamster cage and threatening her with a wooden pallet in front of a child.