Gao Yang's physical condition no longer allowed him to participate in the battle. For the entire day, aside from nibbling on two pieces of chocolate he had managed to get from Nate, he hadn't eaten anything else, and he hadn't had a sip of water. After giving blood to Ivan and losing blood from a gunshot wound, Gao Yang was indeed very weak.
Being unable to fight and forcing himself to go would only burden others, so Gao Yang had no choice but to join the injured, staying in the jungle near the end of the small road.
Although he was injured, Gao Yang had never truly considered himself a casualty. When everyone else set off and he had to stay behind, time seemed to pass exceptionally slowly for him.