Comfortably? Could a boxer out-last a cyclist in an endurance running race? Perhaps that's an unfair comparison. Of course you get quick and nimble boxers, and obviously I'm not trying to claim endurance isn't key in boxing, but I'd guess that a cyclist would out-last a boxer even at peak fitness in an endurance event.
Obviously tennis players are becoming more like boxers "if you want to play better tennis, train like a boxer," and both would destroy each other at certain competitions, but boxers only "peak" a few times a year, and when we are talking about darren fletchers fitness I'd say Paddy Crerand is talking about the wrong sports. Boxers are often unfit.