That would be unusual. Unless he's injecting no-ester testosterone IV (highly unlikely), there will no immediate effect from the shot.
Is it the first shot? That would really make no sense.
Otherwise, maybe he wants to measure the trough level and for some reason of convenience does the shot before the blood draw, with the understanding that the shot will take some time to affect blood levels.
Or (sadly) maybe he doesn't know what he's doing.