The relationship between a football manager and a referee is often a strained one and former official Mark Clattenburg has revealed a tense and bizarre exchange he once had with Jurgen Klopp.
The duo did not always see eye-to-eye in the Premier League when Klopp was at Liverpool, but this incident pre-dates the German's time in England.
In fact, the pair swapped pleasantries for expletives after Clattenburg officiated a Champions League tie during Klopp's spell as Borussia Dortmund boss in April 2014.
As one of England's most experienced referees, Clattenburg was tasked with Dortmund's quarter-final first leg at Real Madrid - which they subsequently lost 3-0.