The singer joined the musician at the Gramercy Park Hotel and sang "Someone to Watch Over Me."
"Thanks to the 1&only @ladygaga for coming out to @GPHhotel tonight an singing a song!!" Newman tweeted after the show at the Rose Bar last Thursday night.
E! said this was Lady Gaga's first time on stage since she was forced to cancel the remainder of her Born This Way Ball concert tour to have the operation in February.
She has not yet announced plans to resume her performance schedule.