12:12 PM PT – It didn’t take the band long to replace Lindsey … in a statement provided to TMZ, the group has announced that Mike Campbell and Neil Finn will join the group for the upcoming tour.

As for the Lindsey situation, the statement simply reads, “Lindsey Buckingham will not be performing with the band on this tour. The band wishes Lindsey all the best.”

Fleetwood Mac has lost a key member of the band just as the group is set embark on a giant tour – Lindsey Buckingham is out … TMZ has learned.

Sources connected to the group tell us Lindsey will no longer be involved in any band activity, and will not be joining his former bandmates on the massive tour this summer.

It’s unclear exactly why he’s splitting from the band – or who cut ties with who – but we’re told, for now at least, the decision is final and firm.

Buckingham served as FM’s lead guitarist for over 40 years, ever since he and then-girlfriend Stevie Nicks were recruited by Mick Fleetwood and co.

After he and Nicks came aboard, the band’s popularity skyrocketed on the heels of two hit albums – 1975’s “Fleetwood Mac” and ’77’s “Rumours,” the latter of which is the 8th best selling album of all time.

Their last headlining show together was last summer.