With only a day until the FireAid benefit concert, the star-studded showcase is getting a shakeup to its lineup ... Dave Matthews has announced his exit from the show.

The singer shared the update on the Dave Matthews Band's official Instagram page Wednesday, where DM confirmed he would no longer be participating in the concert benefiting Los Angeles wildfire victims Thursday ... as he had to deal with "a critical illness in the family."

The "Crash Into Me" singer made it clear he was disappointed to be missing the show ... and also revealed he was "unfortunately unable" to participate in the MusiCares Persons Of The Year event honoring The Grateful Dead, which is set to take place Friday at the Los Angeles Convention Center.

It's currently unclear how this last-minute change will impact the flow of show, given Dave was set to hit the stage alongside John Mayer at the Kia Forum.

Still, there will be plenty of memorable acts during the 2-venue, one-night benefit concert ... Lady Gaga, Stevie Nicks, Gwen Stefani, Green Day, and Billie Eilish, among other huge names, are all still a go to perform at the Kia Forum and the Intuit Dome tomorrow evening.

The MusiCares gig has an equally stacked lineup, with Maren Morris, Noah Kahan, Vampire Weekend and more all scheduled to perform.

So, while Dave may be missed, there's no reason to unload your ticket!!!