A fight between Aaron Carter and Lenny Dykstra is NOT gonna happen ... so says the singer himself, who tells TMZ Sports the ex-baseball star is too old and fragile to step in the ring with him.
As we previously reported, the former All-Star slugger called out the pop star earlier this week ... saying, "I'm gonna f***** take this mother f***** apart piece by piece, okay?"
But, Dykstra's not gonna get that shot ... 'cause AC says he has too big of a heart to fight a 58-year-old man.