Rays superstar Tyler Glasnow melted down in front of reporters Tuesday ... claiming the MLB's new crackdown on foreign substances RUINED his elbow -- and he's now VERY upset about it.

The 27-year-old Tampa Bay ace said when MLB officials hinted at punishing pitchers for rubbing substances on their throwing hand and baseballs ... he was forced to adapt.

Glasnow -- who said he usually uses sunscreen and rosin on his hand to get a grip on balls -- did away with the stuff two starts ago against the Nationals on June 8.

And, while Tyler spun a gem, he said the lack of tack on his hands put strain all over his elbow ... claiming that led to it blowing out in his last start against the White Sox on June 14.

"Waking up after that [Nationals] start, I was like, 'Okay, this sucks,'" Glasnow said. "Something is weird here. And then that same feeling is persisting all week long."

"And then I go into my start [Monday] and that same feeling, it just pops or whatever the hell happened to my elbow. Like, I feel it. Something happens. And I'm sitting up here like, 'You've got to be f***ing kidding me.'"

The Rays say Glasnow was diagnosed with a torn lgiament in his elbow as well as a flexor tendon strain ... and it's now very possible the dude will need Tommy John surgery to recover.

Glasnow made it clear he wasn't using the foreign substances to cheat, but rather to just get a grip on the baseball -- and now he's concerned other pitchers might suffer his same fate because of MLB's sudden, midseason rule change.

"I'm frustrated that they don't understand how hard it is to pitch," Glasnow said. "And to tell us to do something completely different in the middle of the season is insane. It's ridiculous."