Making his 600th appearance for the club in Wednesday's Champions League tie, Ramos was booked late in the game for a foul on Ajax striker Kasper Dolberg.
Madrid were leading 2-1 at the time of the yellow card being shown to Ramos, who will miss the second leg at the Santiago Bernabeu through suspension as a result.
Ramos appeared to initially admit he deliberately earned the booking so he could serve the ban before the quarter-finals, should three-time defending champions Madrid progress.
"Looking at the result, I'd be lying if I said I didn't force [the booking]," he told reporters after the game.
"It is not to underestimate the opponent nor to think that the series is over, but in football you have to make tough decisions."
But Ramos then backtracked on his comments in a post on social media.
"I want to make it clear that it hurts more than anyone, I have not forced the card, as I did not against Roma in my previous Champions League match," the Madrid captain wrote on Twitter.
"I will support from the stands as one more fan with the illusion of being in the quarters."
In a statement released on Thursday, UEFA confirmed Ramos' comments are being examined.
"A disciplinary investigation has been initiated based on Article 31(3) of the UEFA Disciplinary Regulations in connection with the statements made by Real Madrid player Sergio Ramos in the above-mentioned match," the governing body said.
"Information in respect of this investigation will be made available in due course."
In December 2017, Madrid right-back Dani Carvajal received a two-game ban from UEFA after he was adjudged to have deliberately earned a booking.
Carvajal was deemed to have wasted time in the last minute of Madrid's 6-0 win over Cypriot side Apoel Nicosia, acquiring a caution that ruled him out of a group game against Borussia Dortmund, with the Spanish giants having already qualified for the knockout rounds.
Should Ramos be given a similar punishment to Carvajal, he would miss the first leg of the quarter-final if Madrid hold on to their lead against Ajax.