Eight teams have claimed ‘the treble’ over the years, winning the European Cup, league title and biggest domestic cup in the same campaign.
Celtic became the first to do it in 1966/67, a feat subsequently matched by Ajax (1971/72), PSV (1987/88), Manchester United (1998/99), Barcelona (2008/09 and 2014/15), Internazionale Milano (2009/10) and Bayern München (2012/13).
Which clubs are still in the running to join the elite band this season?
Top of Liga, eight points ahead of Atlético
Will face Sevilla in Copa del Rey final on 22 May
Top of Bundesliga, five points above second-placed Dortmund
Host Werder Bremen in German Cup semi-finals on 19 April
Confirmed as Ligue 1 champions on 13 March
Visit Lorient in French Cup semi-finals on 19 April
Will meet Lille in French League Cup final on 23 April
Out of the reckoning …
Second in Liga, eight points behind Barcelona
Knocked out of Copa del Rey quarter-finals by Celta Vigo
Top of Portuguese Liga, two points ahead of Sporting CP
Eliminated from Portuguese Cup in fourth round by Sporting in October
Up against Braga in League Cup semi-finals
Fourth in Premier League, 12 points short of Leicester
Knocked out by Chelsea in FA Cup fifth round
Beat Liverpool in English League Cup final on 28 February
Real Madrid can no longer win a treble
Third in Liga, 12 points short of Barcelona
Excluded from Copa del Rey after fielding ineligible player
Eighth in Bundesliga, 29 points below Bayern with eight games left
Ousted from German Cup in second round by Bayern in October
*League Cups are played in a minority of countries, including France, England, Portugal and Scotland. Celtic, in 1966/67, are the only team to have won a quadruple of European Cup, domestic league, domestic cup and domestic league cup.