It looks like he was in hospital in Malta for about a month and a half, so yes that suggests he was injured rather than suffering some illness. I am not sure whether this was a result of the wrecking of the Manzanita, or whether he was already on board Sapphire. Since I don't think Sapphire was involved in any enemy action at that time, I think it is more likely that John was injured in the wreck of Manzanita and transferred as a casualty to Sapphire which brought him ashore for treatment. What is odd is that after being discharged from hospital to HMS Egmont, and then to Admirable (which was the ship co-ordinating the drifters), he was shown as 'for Manzanita' although she had already been wrecked by that stage.