Matthew McConaughey is taking offense to a surgeon who claimed to have restored Matt's luscious locks via hair transplant ... the actor says it's all a big, fat lie!

Matt fully acknowledges in the '90s he had to shave his head because his hair was getting super thin. Something happened, because when he grew his hair back his mane was enviable.

Matt insists it was NOT the result of surgery. He says he was able to grow his hair back in full force by rubbing topical ointment on his head ... every day.

“I was fully committed, I was fully committed to it — no Propecia, no nothing, it was just manual labor", Matt says in his memoir, "Greenlight.." In fact, he says he's been using the ointment for 20 years.

Mr. McConaughey is ticked off at a Los Angeles surgeon who's taking credit for the hair restoration, claiming Matt went under the knife.

As you can see, the change is quite remarkable. So much so, Mathew reveals ... one surgeon, in particular, noticed and took credit for it.

There were lots of stories that Matt got a transplant, and when he bumped into a different doctor he did a quick once over and agreed with Matt ... he never had a transplant.