It's a weird one because he looked really good against Holloway. McGregor has much better fitness than someone who hasn't fought in 2 years, but there have been question marks over his cardio since the Chad Mendes fight IMO. Round 2 of the Mendes fight, he looked gassed. In the first Diaz fight, he gassed pretty quickly, but that was down to his absurd game plan of trying to take out Nate in the opening rounds (and he got hit with some nasty knees). Second Diaz fight, he gassed badly but found second wind. I think the most suitable explanation - aside from his erratic game plan - against Diaz is that he bulked up for 3 months and didn't invest too much time on his conditioning, and realistically it should take around a year to get used to carrying that muscle around.