Jake, 24, now holds an undefeated professional boxing record of 3-0 after defeating former UFC fighter Ben Askren last weekend.
The American star has insisted that he is serious about his venture into the world of boxing, even saying that he has a documentary about his short-lived fight career in the works.
Jake's brother has now staunchly defended his boxing ambitions as he told his critics to 'stop doubting him.'
Logan, who is expected to fight boxing legend Floyd Mayweather in June, told MMA Junkie: "What the f**k did y'all expect?
"Stop doubting Jake. Every fight I'm like, 'Ehhhh.' Stop doubting Jake."
Jake secured a lucrative payday from his win over Askren as the 24-year-old claimed that the fight had over 1.5m pay-per-view buys.
Logan added that his younger brother should not be seen as that "YouTube kid," saying that he is a "f*****g bad motherf****r."
The 26-year-old American YouTuber explained: "He's not who you think he is. He's not the YouTube kid anymore.
"He's a f*****g bad motherf****r with a heavy right hand. There's a reason [...] no-one can survive those. No-one has.
"And he's gonna continue doing so. Doubt him all you want, but you're gonna be wrong every time."
YouTuber KSI, real name Olajide Olatunji, has insisted that he will fight Jake as he vowed to "f**k him up to show how much of a fraud he is."
Speaking in a YouTube video, the 27-year-old English star said: "I'm going to fight Jake.
"I want to fight Jake. Don't get it twisted. When I saw he knocked out Ben Askren, I got angry.
"There's a part inside of me that feels like I need to f**k him up to show how much of a fraud he is. [...] [But] best believe when we get in that ring, I'm knocking him out."
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