Joe Manganiello says Sofía Vergara took a parting shot as he walked out the door ... he claims she told him no one would love him once they realized how sick he was.

The actor recalls his last interaction with his ex-wife in his new memoir, "Bloodlines" ... claiming Sofía was incredibly angry and hurt when he moved on with Caitlin O'Connor.

Joe says his marriage to Sofía had died out long before this last blow-up ... but the pair had agreed to stay together publicly.

When that part of their relationship came apart, Joe says he decided to leave ... and, on his way out, he says Sofía told him he wasn't as healthy as he might think.

Joe claims she told him he'd get sick again ... and, even worse, he claims she also said that -- in her opinion -- no one was going to love him once they realized how sick he actually was.

It's the latest bombshell from Joe's book ... he also claims Sofía ridiculed him over the serious autoimmune disorder from which he suffered for years.

Sofía's son, Manolo, seemingly took a shot at Joe days before the book's release ... posting about narcissistic men on social media. Sofía reshared the post.

Joe did find love after Sofía ... he is engaged to Caitlin.

We've reached out to Sofía about this alleged exchange ... so far, no word back.