Referee Mark Geiger has "strongly refuted" claims he asked for the shirt of Portugal captain Cristiano Ronaldo at half-time of the clash with Morocco on Wednesday.
The allegation was made by Morocco midfielder Nordin Amrabat after a game in which American official Geiger made a number of calls that were questioned by the north Africans.
Amrabat told Dutch television station NOS: "I do not know what he is used to but he was very impressed with Cristiano Ronaldo and I hear from [Portugal defender] Pepe that he asked Ronaldo in the first half if he could have his shirt.
"What are we talking about? At the World Cup? It's not a circus here."
FIFA responded by backing Geiger and expressing their disappointment at Amrabat's outburst.
In a statement it said: "It is with regret and disappointment that FIFA has learnt of reports in the media concerning the referee Mark Geiger."