Does George Groves have a Glass Jaw?

There are very few world class fighters in boxing history that have a mandible as fragile as Khan's,

 

Someone mentioned stamina issues with both degale and groves. Maybe just me but that jack didnt tire at all. And that was a hard fought fight at pace. We talk about stamina issues but are you not meant to be tired in a fight like that. Tbh i m suspicious if people are fighting on an even playing field. No ones working harder than degale in the gym for example in terms of cardio with a trainer like that. And yet hes tiring in fights and the other guys look like they can go another five rounds. Always seems to be the case when the brits get over to america. Dont want to be pointing fingers but you d be stupid not to raise the question. Whats the differences in the cardio they re doing over there because it seems to be working for them. Froch/hatton/haye/degale/groves. All tired in fights. You could see them tire. Some of these americans arent