Newest updates to the Weezer website said Welsh is currently suffering from a private medical problem.
"We have learned that Mikey has checked into a psychiactric hospital, we think in his hometown of Boston. However, we unfortunately still dont know whats wrong with him, and continue to find it very difficult to find out any more from those who might know. We wish him the very best and we hope he comes back soon. But in the meantime, due to the circumstances at hand with the upcoming tours and such, we are indeed hastily scheduling try-outs for a replacement player for the upcoming gigs, JUST IN CASE Mikey isn't able to return."
The rest of the band are rehearsing for a tour and working on other projects.
New images and diary reports of the new Weezer single promo video for 'Island In The Sun' also appear on the offical website