Jake Paul Smokes Cigarette While Training For Nate Diaz Fight

Jake Paul isn't worried one bit about having to go 10 rounds with Nate Diaz in August ... and he made that crystal clear by smoking a heater during a recent training session!!

The Problem Child shared the funny footage to his Instagram page on Monday ... showing him hitting the bag and ripping a cigarette while training in Puerto Rico.

"Getting my lungs ready for 10 rounds," Paul said. "August 5th. #PaulDiaz"

The two sides recently agreed to make the fight longer than the initial eight-round agreement ... which will make it the longest bout in both Paul and Diaz's careers.

Now, it's likely the 6-1 boxer pulled a Bill Clinton and didn't inhale anything ... but the message was still pretty obvious -- he's ready to go all 10 rounds against the former UFC star.

One thing's for sure, though -- Jake's opponent is no stranger to smoking, and he's very open about his love for cannabis ... so it could very well be a shot at Diaz.