Brock Lesnar's longtime friend and Jiu-Jitsu coach tells TMZ that the UFC Heavyweight champ WILL return to the Octagon -- within 6 months.

Rodrigo "Comprido" Medeiros, a 7-time World Jiu-Jitsu champion, told TMZ that Lesnar "is getting better and that is the most important thing ... He will be fine and be fighting again within 6 months."

Medeiros added, "I can just say that the heavyweights can stop laughing and get ready to start crying because the champion will be back soon."

Lesnar had surgery earlier this week to repair a hole in his intestine. While Lesnar is still in rough shape and has a long road ahead of him, the outlook has improved dramatically from last week when Dana White was saying that Lesnar is "very very sick" and may never fight again.