Sherri Shepherd Baby -- Lawsuit Threat ... If She Abandons Unborn Kid

Sherri Shepherd will be sued if she doesn't embrace the child she's having this month via surrogate ... so promises her very angry and determined estranged husband.

We've learned Lamar Sally is already drafting legal docs to prevent Sherri from backing out of the surrogate contract she signed while they were still a couple.

As TMZ first reported ... Sherri claims Lamar defrauded her into signing the contract ... claiming he knew he wanted out of the marriage but wanted to hook her into paying child support. She wants the contract voided on grounds of fraud ... and wash her hands of any parental obligations.

Lamar is calling BS and says he'll fight to put Sherri's John Hancock on the birth certificate ... and if that takes a judge's order, so be it.

We're told Lamar may weave what he believes is Sherri's hypocrisy into the contract, saying on the one hand she professes to be a good Christian and on the other abandoning an innocent child.