Jurgen Klopp "had to wait" as controversy almost derailed Liverpool's Villarreal plan

Liverpool's upcoming Champions League semi-final against Villarreal isn't their first high-profile meeting with the Spanish side, and nor is it their first collision course with manager Unai Emery in European competition.

Back in 2016, during Jurgen Klopp's first season in charge, Liverpool came from behind to beat the Yellow Submarine in the Europa League semi-final, only to lose to Emery's Sevilla in the final in Basel. However, the Reds' had to face both sides without centre-back Mamadou Sakho after a drug test controversy which rumbled on for years.

The French international was sidelined as the Merseyside club investigated "a possible anti-doping violation," leaving them without a man who played a big part in their European run. The defender would later end up suing the World Anti-Doping Agency (WADA) over the incident, but the resolution came long after Emery had got the better of Klopp and added a third straight continental title to his and Sevilla's trophy cabinet.

It all began with a last-16 game against Manchester United - a fixture which was already notable for being the first ever meeting between the giants in UEFA competition. The Reds had progressed thanks to a 2-0 home win and a 1-1 draw at Old Trafford, but Sakho was found to have failed a doping test after the second leg.

The French defender had played the full 90 minutes of the away leg, partnering Dejan Lovren in central defence, and the pair also played a huge role in the quarter-finals before the alleged offence was made public. With the Reds needing three goals in the final 30 minutes against Borussia Dortmund, both centre-backs were on target in a momentous comeback.

“I wasn't there, but I told the lads in the dressing room at half time we