weak as a baby
(as) weak as a baby
Especially weak, feeble, and vulnerable. The heart attack left me bedridden and weak as a baby for nearly a month. You'll always be as weak as a baby if you stay inside playing video games all the time!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
*weak as a babyand *weak as a kitten
Cliché [of someone] physically very weak.(Also: as ~.) Six weeks of illness left the athlete as weak as a baby. John is as weak as a kitten because he doesn't eat well.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.