This happens during the first cutscene, where the squad is in the boat and the player hears the commander's directions over the radio. A squad member reports that "we got a man down". It can be heard but it's not written in the radio chat log. I assume it can be some kind of penalty for loosing squad members before, but if it's so then it's not well implemented. I've lost four men in "Bingo Fuel" who weren't originally in the squad. I had four men in the squad before the "Attention Deficit" mission, after I finished the "Bingo Fuel" (8 - 4 = 4). Nevertheless, I had only one medic in "Attention Deficit" and noone else. Seems quite wrong...