As Barcelona can attest, the Champions League knockout rounds are an unpredictable beast that can throw up plenty of surprises, such as, for example, an old player returning to bag a crucial goal.
And as Real Madrid prepare to host Napoli on Wednesday night, Zinedine Zidane will be wary of ex-Madridista Jose Callejon's presence in the Partenopei ranks, the forward having enjoyed a long academy career in La Fabrica before returning for a productive spell under Jose Mourinho.
As a player, Zidane watched on as one of the most infamous moments in Los Blancos Champions League history unfolded, provoked by a returning Real striker in the shape of Fernando Morientes.
In the 2003/04 quarter-finals, the Frenchman had just made it 4-1 in the first leg at the Bernabeu before a Morientes strike added a vital away goal that helped Monaco to a 5-5 aggregate win via the rule, the forward adding another in the return match.
The precedent was set for Alvaro Morata, now back in the Spanish capital, to deal Real their most-recent European exit in the 2014/15 semi-finals, scoring in both legs of a 3-2 victory for Juventus.
In fact the list of ex-Madrid players coming back to haunt Los Merengues is rather extensive; Klaas-Jan Huntelaar, Wesley Sneijder, Roberto Soldado, and Joselu are to name just a few.
But Samuel Eto'o has been the most prolific, the Cameroonian forward scoring twice to take the 2003/04 LaLiga title out of Real hands as part of his 10 strikes against Los Blancos.
