Angus Young admits Phil Rudd had been acting "strangely" before his arrest.
The AC/DC drummer was arrested earlier this month and will appear in court on Thursday (27.11.14) to answer charges of making threats to kill and possession of illegal substances and his bandmate believes the musician had been having problems for some time.
Angus told Triple M's The Grill Team: "He's in a strange place, in a strange situation
"It's something we have to get resolved, if we're going forward, something has to get resolved.
"We had a few problems ourselves before he got into this situation. There was a lot of strange behaviour going on. I guess you could put it down to him just not showing up for a lot of what we were doing and when you have to get to a stage where you have to convince someone to be there, you know it wears thin after a while - but it's something we have to resolve."
The group are planning to tour their new album 'Rock or Bust' next year but are unsure whether the troubled rocker will be joining them on the road.
Angus admitted: "It is a bit of a question mark...we go back a long way, he is a great drummer, but I think over these last few years, I don't know what he's got into or anything - I guess it doesn't help the situation that he's in."
AC/DC were further shaken this year when rhythm guitarist Malcolm Young - Angus' older brother - had to be admitted to a care home after developing dementia.
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