Francis Ngannou returned to the cage last weekend -- 6 months after tragedy struck his family -- and the combat sports superstar admits he was unsure whether he'd ever fight again.

TMZ Sports talked to the 38-year-old former UFC champion turned boxer/PFL fighter just days after he dispatched Renan Ferreira via a first-round knockout in Saudi Arabia ... and then broke down in tears after the bout while talking about the devastating loss of his little boy, Kobe.

"Oh, yes [I didn't know if I'd fight again]. There was a point that you didn't know anything. Everything seemed so fragile," Francis told us, adding his mind was racing a mile a minute during that horrific time.