Meaning of "I would not have a leg to stand on, I suppose"

hi,

plz explain me the meaning of “i would not have a leg to stand on , i suppose.”

thanks

not have a leg to stand on

to be in a situation where you cannot prove something:

[i]The problem is, if you don’t have a witness, you don’t have a leg to stand on.

I haven’t even got the receipt to prove where I bought it, so I don’t have a leg to stand on.[/i]

(from Cambridge International Dictionary of Idioms)