When Ed McMahon's Next Big Star premieres Sunday (6 pm/ET on PAX), its titular host promises a competitive showcase for up-and-coming talent — much akin to Star Search, his popular 1980s series — as well as appearances by established entertainment superstars. (Steven Tyler, 'N Sync and Jessica Simpson, to name just a few, have already taped segments.) Yet one friend of McMahon's that you won't see is Johnny Carson, the Tonight Show host for whom McMahon served as announcer and sidekick for three decades.

"It's very unlikely," McMahon tells TV Guide Online of the possibility for a cameo by Carson, who largely has been MIA since turning over the late-night talker to Jay Leno in 1992. "He just won't do anything on television.

"Johnny has turned down hosting the Oscars five times," he adds, illustrating his point. "And that would be the show to host, with three billion people watching."

Instead, McMahon hopes that Next Big Star will discover — and, where warranted, catapult the careers of — a new generation of comedians, vocalists and musical groups. "In February, when I launched the Internet component of this show," he relates, "I took 3LW — then brand new — on a 40-day bus tour. Afterwards, they launched their album, which immediately went gold. So it's a pretty effective format, I tell you."

There's no arguing that point, in light of the list of Star Search alumni. Boasts McMahon: " Ray Romano, Drew Carey, Martin Lawrence, Christina Aguilera, Britney Spears, Justin Timberlake, Alanis Morissette, Aaliyah, Destiny's Child. They all came out, did their thing and did it right, and off they went!"