FIFA released a statement on Thursday, supporting US referee Mark Geiger, who had been accused of asking for Portugal captain Cristiano Ronaldo's shirt during the team's World Cup match against Morocco.
The Group B encounter was officiated by Geiger and finished in a 1-0 victory to Portugal at Moscow's Luzhniki Stadium on Wednesday.
Later on Wednesday, international media quoted Morocco forward Nordin Amrabat who said that he heard Portugal defender Pepe say the referee asked Ronaldo if he could have his shirt after the first half.
"It is with regret and disappointment that, following Wednesday's Group B game between Portugal and Morocco, FIFA has learned of reports in the media concerning referee Mark Geiger. It has been claimed that Mr Geiger asked for the shirt of the captain of Portugal during the half-time interval. Mr Geiger strongly refutes these claims and categorically states such a request was not made," FIFA said in the statement.
FIFA also called on the teams to respect all principles of fair play.
"FIFA unequivocally condemns the allegations supposedly made by a member of the Moroccan team. FIFA referees are under clear instructions with regard to their behavior and relationship with the teams at the World Cup and it can be confirmed that Mr Geiger has acted in an exemplary and professional manner as an appointed match official," world football's governing body added.