"Everyone at Rangers is deeply saddened by the news of the passing of one of our supporters, which occurred overnight in Porto due to natural causes. Our thoughts are with the victim’s family and friends at this very difficult time, and we are in contact with both the Portuguese and British authorities," the club wrote on its official website.
Although they were already out of contention in the competition, many Scottish fans travelled to northern Portugal to watch the match, which kicks off at 20:00 GMT at Estádio do Dragão.