La Liga is using a lip-reading expert to investigate a comment Real Madrid's Jude Bellingham is alleged to have made towards Getafe's Mason Greenwood during Thursday's game.
La Liga says Getafe "filed a formal complaint" and will "act based on hard evidence".
The incident came after England international Bellingham tackled Greenwood during Real's 2-0 win.
A clip of the incident then went viral on social media.
It is not clear to whom Bellingham made the alleged comment.
In a statement on Friday, La Liga said: "Yesterday, Getafe filed a formal complaint with the La Liga match director who, as per standard procedure in such cases, has requested an expert lip-reading report to investigate the matter and act based on hard evidence."
Greenwood, 22, joined Getafe on a season-long loan from Manchester United on 1 September.
In August, United said the one-cap England international would leave the club by mutual agreement after a six-month internal investigation into his conduct.
It came after charges against the player, including attempted rape and assault, were dropped in February.
Greenwood whose contract at old Trafford runs until 2025 has scored six goals in 21 appearances this season
Bellingham, 20, joined Real Madrid in the summer for 103m euros (£88.5m) and has 18 goals in 27 appearances for lost blancos