"Workaholics" star Blake Anderson seriously injured his anal area last month when he jumped off his roof onto a beer pong table -- this according to the 911 call placed the morning after the stunt gone wrong.

As we previously reported, Blake fractured his spine during the accident -- which occurred at a raging house party at the actor's L.A. house in December -- and he subsequently required back surgery.


According to the caller -- Blake's dad -- Blake plummeted 20-25 feet during the fall, adding, "He landed on his feet but now he's having extreme pain around his lower back area and his buttocks ... to the point where he can't walk." His dad clarifies, "There's a stabbing pain around his anal area."

The dispatcher asks how Blake fell -- and Blake's dad blatantly lies ... claiming the actor "stumbled."

But as you can see in the video, Blake did NOT stumble -- Blake took a flying leap off his roof while the crowd chanted, "Blake! Blake! Blake!" He then crashed, ass first, through a beer pong table.

Live and learn.

Blake Anderson -- the frizzy-haired guy on "Workaholics" -- fractured his spine Saturday night ... jumping off his roof onto a beer pong table ... and the incredibly stupid stunt was all caught on tape.

Sources close to the actor tell us, he's currently undergoing surgery to treat the fracture -- and fix whatever else he messed up. Needless to say, he'll be out of commission for a few months.

Blake was throwing a party at his L.A. house when the accident went down -- attended by Tyler the Creator and members of his rap crew. We're told cops shut the entire thing down not long after the roof-jumping.

The lesson here kids ... DON'T JUMP OFF YOUR ROOF!!!!!!!