The group is auditioning potential replacements for Mikey Welsh, who has checked himself into a psychiatric hospital with an undisclosed illness. It’s not clear if he’ll be ready to join what will likely be a lengthy tour set to start September 11 San Jose, Calif..

It took a while for Welsh’s bandmates to figure out what had happened to him. The rest of Weezer discovered he had missed a plane flight August 14 when he did not arrive in California for a video shoot. At the time, Welsh was said to be suffering from a “private medical condition.”

They had a bit more info on the 16th. “We have learned that Mikey has checked into a psychiatric hospital, we think in his hometown of Boston,” a band rep wrote on their Web site.

“However, we unfortunately still don’t know what’s 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.”

Meanwhile, Weezer’s fall tour – with hard-rockers Cold in the support slot – is taking shape and more dates should be confirmed soon. They’re reportedly rehearsing a bunch of new songs and maybe fans will get to sneak preview some new material during the shows.

The band is offering Internet-only ticket pre-sales “designed so the online Weezer fans can get early access to tickets before the public on-sale.” Details are available at weezer.com.