A spokesman for the show confirmed that Bart — who plays Frederick Frankenstein — has missed some performances of the show since the Oct. 13 matinee.
"He is responding well to treatment and is expected to return to the show shortly," according to a statement.
Ensemble member and understudy Matthew LaBanca (making his Broadway debut) has gone on for Bart, and will continue to do so until Bart returns. No official return date has been announced.
Bart is a Tony Award winner for You're a Good Man, Charlie Brown (he played Snoopy) and was Tony-nominated for playing Carmen Ghia in Mel Brooks' The Producers. He also starred in Lincoln Center Theater's The Frogs. His film and TV credits include "Desperate Housewives" and the "The Stepford Wives."
Bart played the heir of the Frankenstein family in the world premiere of the musical comedy in August at Seattle's Paramount Theatre, where a tryout ran for a month before the cast and crew headed back into September Manhattan rehearsals toward an Oct. 11 first preview.
Susan Stroman directs and choreographs the new musical based on the hit film comedy that had a screenplay Mel Brooks and Gene Wilder. Brooks and Meehan penned the new musical's libretto; Brooks wrote the music and lyrics.
Young Frankenstein is scheduled to officially open at the Hilton Nov. 8.
Matthew LaBanca appeared in the Children and Art gala at the New Amsterdam Theatre, toured as Simeon in Joseph and the Amazing Technicolor Dreamcoat and appeared in productions at Paper Mill Playhouse, Theater Under the Stars. He also toured nationally in productions of Crazy for You and Anything Goes.