Allen, who won the Fox show's eighth season, praised Sanchez's talent on Ryan Seacrest's KIIS-FM radio show.
"I think Jessica is, like, by far one of the best singers that's on the show," he said. "If not that's ever been on the show."
Allen added: "She's bananas."
The judges used their save earlier this month when Sanchez finished bottom of the viewer vote on American Idol.
At the time, judge Randy Jackson described Sanchez as "one of the best singers in America ever".
American Idol continues tonight (April 25) at 8/7c on Fox.