Johnny Damon Got a SECOND Vasectomy

There will be NO EIGHTH CHILD for Johnny Damon ... 'cause the ex-MLB star says he just got snipped for the second time ... after his first vasectomy didn't quite hold up.

The former Red Sox stud was at the Mohegan Sun 20th Anniversary party with his wife, Michelle -- when they were asked if they were planning to add another Damon to the already massive family!

That's when Johnny revealed that he already tried to put a stop to his procreating with a vasectomy a few years ago -- but it didn't work ... and Michelle got pregnant with his 7th kid!

Damon says he had to go back and have a doctor rework his man plumbing -- "Hopefully, this one worked."

FYI, Damon's kind of an anomaly -- 'cause less than 1 PERCENT of vasectomies fail the first time ... according to Healthline.com.