Champion cannot be targeted underneath a tower

I recently had a game that could have been won with an ace but resulted in a penta for the enemy champion Varus when he stood directed underneath a tower and no one could target him it only prompted to attacked tower. I don't see many mistakes but this one really irked me. I tried to take my time to target but there was no possible way since I only saw his outline underneath it. Please add any comments to help bring this to riots attention. I already sent in a ticket about the issue and redirected me to post onto here. I don't usually see any really bad bugs in the game, but this mechanic didn't ruin 1 person's game, for it ruined 5.