We talked to the 33-year-old fighter from Boston just days after his unanimous decision win of Chikadze ... and asked if he believes people disrespected him leading up to the fight ... and while Kattar agrees, he's more irked by Giga's seemingly lackadaisical attitude.

"I took more offense to my opponent kinda overlooking me. Calling out the champ when he has a fight with me in about a week. It just seemed like he was overlooking me, and like I've mentioned before. If that's the case, not smart, and you're probably gonna pay for it, and he did."

FYI, Giga was previously ranked 8th in the division before the fight (Calvin was 5th) ... but Kattar was coming off a big loss to Max Holloway, and Chikadze was undefeated in the UFC (now 3 losses overall).

That's why Giga was more than a 2 to 1 favorite.

Kattar continued on Chikadze ... "I didn't like the way he overlooked me and was looking past me and focusing on people he might fight rather than the guy he was gonna fight. That's never a good idea."

What's next for Kattar? He says he's down to step in for either Volkanovski or Korean Zombie in April at UFC 273 ... if either man is unable to make it to the cage.

"I think if something happens to that fight, I'd be a good fill-in, for sure."

If not, Kattar says he'd "like to fight up" ... meaning he wants to fight a higher-ranked fighter, as he continues his trek to the top.

"Whoever's next is fine with me, man, I just hope it's more big moment opportunities, more main events, bigger paydays, on my way to just changing my life and chasing that life on the other side of a win."