Songwriter and producer Dr. Luke was set to judge the singers on the Fox television show, which is scheduled to begin taping in September, but withdrew from the show Aug. 23 because "Idol" would be too big of a time commitment.
Connick Jr., who has been seen on the show as a guest mentor, is likely to join Keith Urban and Jennifer Lopez on the judges panel, although Fox had hoped to add an industry professional to the mix.
Connick Jr. was Tony-nominated for his performance in The Pajama Game and the score of Thou Shalt Not.
"American Idol" will return for its 13th season in January 2014. Visit AmericanIdol.com.