In recent weeks, James Levine appeared to be on the mend from his latest round of medical troubles, but he has suffered another setback. On Thursday, the conductor withdrew from a performance of Die Walküre, saying he was ill. Yesterday brought a flurry of cancellations: the Met announced that Levine would not join the company's forthcoming tour of Japan or lead a Met Orchestra concert on May 15 — Fabio Luisi will take his place — and the Boston Symphony said that Levine would not appear at Tanglewood this summer. All that remains on Levine's schedule for the coming months is a pair of Walküre performances, on May 9 and 14. He will take time to recuperate from recurring back problems, and, it is hoped, return to the podium for Don Giovanni in October. In today's New York Times, Daniel Wakin reports that the Met is now describing Luisi as Levine's "likely" successor. There will be an extraordinary atmosphere in the house for Levine's final appearances of the season, if in fact he is able to conduct. This is a very sad moment, and everyone wishes Levine the very best of luck in his recovery.