Not Eating New Piggy Not Eating - Health Issues or Settling In?

Hello! I recently "rescued" a male cavy (he was abandoned at a pet store and kept in a back room for almost two months) and he seems healthy overall, but he is very shy. While I expected any new guinea pig to be shy, not quite this shy. It might just be his personality and he might just take some opening up, but he is in his hidey-house whenever I go into his room, and often his food is left untouched. This brings me to why the title is what it is - he barely eats his pellets, doesn't eat much of his hay, and won't normally eat his veggies unless I hand-feed him. Is this him just settling in or is there a bigger issue going on? I can elaborate further if needed. Thanks!