The illegal injections were not intravenous, they were subcutaneous injections under the layer of skin on (most likely) their stomach.A painkilling injection is injected to the site. The illegal injections would have been injected into the easiest vein. Pretty sure the senior experienced player could tell the difference between the two. You trying to tell me that the senior players didn't know what was going on?
This delivery method can also go towards determining what substance it was as different substances have different injection methods i.e. intravenous, intramuscular or subcutaneous.