Loureiro stepped back from touring duties in August to deal with family issues. On his recommendation, Megadeth brought in Finnish guitarist Teemu Mäntysaari as a temporary replacement.
But Mäntysaari will now continue as lead guitarist, with Mustaine and Loureiro releasing statements confirming the absence will be extended.
Mustaine says: "Kiko had to leave the tour last August to handle some very important and private family business. He was conflicted but appreciative when I told him that he needed to go to take care of his family. He agreed but was still concerned about us — meaning the fans, and Megadeth.
"Kiko is a top-notch professional, a maestro — and he did not want to hurt me or Megadeth. We came up with a solution to find a fill-in for him during that time and that's when he presented and trained Teemu Mäntysaari to take over for us. In the beginning, this was only going to be until the first week of October 2023. However, things rarely turn out the way they are planned.
"The 2023 tour is over, and it was long and arduous. Last year saw a substantial amount of touring, and it appears that 2024 is gearing up to be even more intense, with extensive touring commitments keeping us on the road for most of the year.
"We have had many conversations with Kiko about this and they have all been very positive. Kiko is going to remain on an extended leave of absence, due to our heavy touring commitments next year and we are going to continue to move forward with Teemu Mäntysaari."
While Mustaine's statement doesn't say definitively that Loureiro has left the band permanently, there is a finality to his words and to the statement made earlier by Loureiro himself.
Loureiro said: "My nine years with Megadeth have been an unbelievable journey, filled with countless 'pinch-me' moments. Unforgettable tours, a Grammy Award for Dystopia, a Grammy nomination, and various accolades for The Sick, The Dying, And The Dead are just a few of the highlights.
"It is hard to put into words the magnitude of these experiences. I am sure any heavy metal fan can appreciate how incredible it is to play and create music in a band you grew up listening to, and to share the stage with a guitar legend like Dave Mustaine, along with phenomenal musicians like James LoMenzo and Dirk Verbeuren, not to mention our incredible crew.
"However, the most cherished aspect of these nine years has been getting to know the incredible army of devoted Megadeth fans around the world. Your dedication is inspiring, and I have immense admiration and respect for all of you."
Loureiro joined Megadeth in 2015, replacing Chris Broderick.
Official statement from @DaveMustaine and Megadeth. pic.twitter.com/DivNwheOWPNovember 21, 2023