Both Real Madrid and Barcelona need a miracle this week if they are to reach the final of the Champions League.
Yet already this season Lionel Messi and his Barca team-mates have proved the unlikely is possible when they overturned a 2-0 first leg defeat by beating AC Milan 4-0 at the Nou Camp.
They will need to do even better on Wednesday when they must overturn a 4-0 first leg defeat against Bayern Munich.
Real Madrid's task is easier - but not much. They trail Borussia Dortmund 4-1 from the first leg, but at least have an away goal to cling on to when they play at the Bernabeu tonight.
Few are giving the Spanish sides any hope of reaching next month's Wembley final, but as this guide proves, anything is possible in football.