The much-anticipated 40th anniversary tour of legendary group Yes has been canceled due to medical problems that lead singer Jon Anderson is currently dealing with.

Anderson reportedly suffered a serious asthma attack in May and has since been diagnosed with acute respiratory failure. He has now been ordered by his doctors to rest up for a minimum of six months or run the risk of further complications.

In a statement issued by Anderson he says: “”I’d like everyone (to) know how deeply disappointed I am by this turn of events. I was looking forward to celebrating our music with the amazing family of Yes fans once again; but as we all know, health must come before anything else.”

Chris Squire, bass player for the group was reported to be particularly sorry for the inconvenience and expense that some fans may have to endure after making hotel and travel reservations that may not be refundable. Ticket refunds, however, will be issued.

So far there has been no word on whether he tour might be rescheduled or if it will take place at all.

For more info see the Associated Press article.