When did Connor do a cruciate ligament? I've never heard that he injured his ACL. I heard he injured his medial collateral ligament, sprained or a minor tear.
I hadn't heard that he had torn his ACL, and was it torn, or a tear? I'd be very, very shocked if he was able to fight with it torn. A tear is about managing pain because mechanical stability remains, if it was completely torn, you can step wrong and your knee buckles in some of the more horrendous pain you will ever experience. You can compete with a torn ACL, but it almost certainly requires an ACL brace to support the joint. The ACL managed front/back stability. It means that without something supporting the knee, if you run and stop the knee buckles. If you plant wrong, it buckles. Pretty much any sort of high impact activity and the knee buckles.
I have first hand experience with competing in sports with a fully torn ACL, and I rocked an ACL brace for an entire basketball season before getting it reconstructed. Like competing with a tear it's a question of how much pain will you tolerate, but the difference between basketball and MMA is, in basketball you can correct the mechanical stability issues by using a brace, in MMA you can't and if you completely blow out your knee in an MMA contest, you're fecking done, no matter who you are.
Carlos Condit is one of the toughest most pain tolerant SOB's in the game, and he tried to deal with it and folded up like an accordion.