CM Punk -- WWE Calls BS on Lump Claims ... Points to 'Rumble' Video

The WWE says it has proof that CM Punk NEVER had a baseball-sized lump on his back at the Royal Rumble -- and insist they have the video that shows he's lying through his singlet.

Punk first brought up the alleged lump on a podcast back in November -- when he claimed he was misdiagnosed by a WWE ringside doctor ... and it eventually led to a life-threatening staph infection.

The doctor filed a $1 million defamation lawsuit against Punk -- and now, the WWE is making it clear they have the doc's back.

"WWE continues to have the utmost confidence in the ability and expertise of our world-class team of physicians, including Dr. Amann," the organization said in a statement.

This is where it gets aggressive ...

WWE says it completed a full investigation into Punk's allegations and made the following conclusions:

-- "CM Punk did not discuss this alleged condition with WWE’s team of physicians and trainers, nor did he discuss it with anyone in our Talent Relations department. WWE has no medical records documenting this alleged condition.
-- The first time WWE was made aware of this alleged condition was when we received a letter from CM Punk’s attorney on August 22, 2014 after WWE terminated his contract.
-- "There is clear video evidence from the 2014 Royal Rumble, which allows all to decide whether there is any appearance of a baseball-sized growth on CM Punk’s back."

Check out the clip ... you seein' a lump?