I don't think that he has medical condition, it's just that he has having a hard time losing weight that is why he have trouble with his body thus resulting in him being admitted to the hospital.
I think that's a better idea if there's still some plans to go to US instead of England. The weariness of his body and just after he has recovered, flight after flight might just give his body tiredness.
I agree that it would be wiser to train in the place where the fight will happen but Team Casimero is working on a limited budget here.
It will entail a huge cost if he set-up a training camp in England as he have to bring in his nutritionist which by the way is in the US who is also busy doing some other stuff.
I think they will fly to the venue two weeks before the fight to get acquainted with the harsh weather of England hehe.
But if that's their strategy, I know that they know what's best for Casimero's situation if they have to go to USA first before proceeding to England.