Like many artistic fields, the opera world loves a star. But for opera singers, their instrument can be more fickle than stardom.

This can lead to some unexpected breakthroughs for some who have not yet been graced – or saddled -- with the title of Next Big Thing.

One of the world's leading tenors, the wonderful Rolando Villazón, has unfortunately had some vocal problems in the past few years. He has a sure, ringing voice, a commanding, engaging and intelligent stage presence. But two years ago he took a year off to give his voice a rest, and now he is out of commission for another six months because of a vocal cyst.

That has opened the door to some somewhat lesser-known, but exciting, singers.

One of them is the young Maltese tenor Joseph Calleja. I first heard him on two recordings he did, a 2004 solo recital disk, Tenor Arias, and another, The Golden Voice, from 2005. Both showed him to possess a lovely, effortlessly musical voice.

But when Calleja stepped in at the Metropolitan Opera for Villazón recently as Nemorino in Donizetti's L’Elisir d’Amore, he demonstrated a winning stage presence and great comic élan. His voice was even stronger and more assured than on his recordings. And his performance of that operatic chestnut "Una Furtiva Lagrima" brought the house down. That's saying something: Even in this age of the automatic standing ovation, it is still rare to hear such ardent cheering at the Met for a relative unknown.

I have to admit it was a thrill. I think I was witness to the birth of a new opera star (let's hope that doesn't jinx him).

Calleja will undoubtedly appear at the Met in coming seasons. But next week he's in Rigoletto in Zurich and later in May, in La Bohème at Munich's Bavarian State Opera. Lucky British opera-goers will be able to see him as Alfredo in La Traviata at Royal Opera House in Covent Garden in June and July.

Mr. Villazón's absence has also led the Los Angeles Opera to cast another tenor, Giuseppe Filianoti, to replace him as Nemorino in its season-opening production of L’Elisir d’Amore, Sept. 12 to Sept. 30. (Covent Garden audiences can hear him this month in the same role). This isn't the first time Filianoti has stepped in for Villazón. Back in February, the Metropolitan Opera had him replace Villazón alongside Anna Netrebko in Lucia di Lammemoor. Critics praised his virile, bright voice, some comparing him to Neil Shicoff.

Now the Met has not yet named a replacement for Mr. Villazón in its December production of Hoffman's Les Contes d’Hoffmann. Can I suggest either Calleja or Filianoti?

I want Villazón to recover as soon as possible and return to the stage and the recording studio. He's too fine an artist, too magnetic a performer to miss. But I think there's plenty of room for terrific up-and-comers like Calleja and Filianoti.

Let's hope their voices stay healthy.