Klopp questioned the awarding of a penalty to Napoli which he felt proved decisive as Liverpool started the defence of their Champions League crown with a 2-0 defeat in southern Italy.

The Reds lacked a cutting edge but would have been worthy of a point at the intimidating Stadio San Paolo, only for the Group E opener to hinge on Jose Callejon being upended in the area by Andy Robertson.

Dries Mertens converted from the spot in the 82nd minute before Virgil Van Dijk lost the ball on the edge of the area in stoppage time, allowing former Tottenham striker Fernando Llorente to seal a 2-0 win for Napoli.