Ellefson left the thrash metal pionners in May after denying allegations that he groomed an underage girl online.
He subsequently admitted to “four to five masturbating encounters” online with a young woman in a police report which surfaced last month.
Mustaine, who previously said that Ellefson would not appear on the record, has now confirmed that a new bassist has completed his role on the album.
Addressing a fan named Tina on Cameo, Mustaine said, per Blabbermouth: “I hear you’re a big pretty fan of [the Megadeth song] ‘Fatal Illusion’ right now. That’s cool. Actually, we’ve got one song on the new album – it’s called ‘The Dogs Of Chernobyl’ – which is very similar to ‘Fatal Illusion’ in aggression.
“So I hope you like that song when you get the new record. It won’t be long. It’s a matter of finishing the parts when I get home today and tomorrow. Our bass parts are all done. And it won’t be long.”
Outlining plans to replace Ellefson on the record, Mustaine previously told fans on Gimme Radio: “I just wanna thank you for all the kinds words and support as we get ready for this next tour and continue to hunt for a new bass player.
“We are making progress. The record’s being completed, and we’re gonna have someone coming in in a couple of weeks to replace the bass tracks that we had. Which should be relatively quick because the person we’re talking to is a stellar bass player. And hopefully this will be an ongoing thing after the recording. Or we will find someone prior to the recording that will be our permanent guy going forward.”