Fulham boss Martin Jol was angered by home fans jeering Bryan Ruiz.
Ruiz, signed to much fanfare from FC Twente in 2011, has struggled this term and his 74th-minute substitution in defeat to Manchester United was met by loud cheers, followed by boos.
And Jol was angered by his treatment.
"It was very disappointing," Jol said. "That [kind of abuse] is something I can cope with because I know football. I have been involved in 1,300 games and I know if people are not happy, they will give you stick.
"Bryan is a player that came back from Costa Rica's game against Mexico, he scored, they won 2-1 and he goes to the World Cup.
"Then to come here and get that sort of contradiction [in reception]: over there he is a hero and here they boo him off the park.
"That is very, very frustrating for him and very disappointing for me. I wanted my supporters to stay behind my players.
"He is an unbelievably nice person so I had to whisper a few words in his ear.
"I said he is arguably my best player and that he should know that.
"It doesn't mean anything but at least a couple here, and I am one of them, trust him."
