Liverpool boss Jurgen Klopp allegedly 'angered' Atletico Madrid with accusations of diving during their Champions League clash on Tuesday night.
An early goal from Saul Niguez condemned Liverpool to a rare defeat, putting the reigning European champions under pressure ahead of next month's reverse fixture at Anfield.
After the game, Klopp claimed that he had substituted Sadio Mane at half time as he feared that the Senegal international would be handed a second yellow card, suggesting that Atletico would attempt to get the winger dismissed.
According to ESPN, the comments annoyed the Spanish giants, who feel that Klopp should have been 'gracious' in defeat.
Given the short margin of victory ahead of the second leg, Klopp also felt that Atletico 'over-celebrated' at the full-time whistle.
Liverpool play host to Diego Simeone's side on March 11.