Referee Jose Luis Munuera Montero says Real Madrid midfielder Jude Bellingham (21) was sent off at Osasuna for abusive language directed at him.
Bellingham has denied the claims after he was shown a red card in the first half of Saturday's 1-1 draw.
Munuera Montero wrote in his referee's report: "In the 40th minute, Bellingham was sent off for the following reason: For addressing me, while I was just a few metres away, in the following terms: 'F*** you'."
If Munuera Montero's report stands, Bellingham faces a lengthy ban.
The rules state: "Insulting, offending or using insulting terms or attitudes towards the main referee, assistants, fourth referee, directors or sports authorities, unless it constitutes a more serious offence, will be punished with a suspension of four to twelve matches."