Madrid's talismanic skipper teased the UFC superstar with a message from Madrid's gym, suggesting he would jump at the chance to take on the Irishman.
Hit by a hamstring injury and absent from the squad that travelled to Kiev to face Shakhtar Donetsk on Tuesday in the Champions League, Ramos has been making good use of Madrid's weights room.
He posted a picture of himself, topless and grinning, walking through the gym as he flexed his muscles.
Both Ramos and McGregor are heavily tattooed and often bushily bearded, and the Madrid skipper captioned his video: "When you're ready, @thenotoriousmma."
That was followed by a winking emoji, with Ramos probably well aware he would come off second best in the Octagon against the man from Dublin.
McGregor (22-4-0) is currently in training for a UFC comeback, having done a U-turn on the retirement he announced in June.
He will fight against American Dustin Poirier on January 23 in a rematch of their September 2014 bout at UFC 178, with the clash expected to happen in Abu Dhabi.
Ramos, meanwhile, was recently named among the 11 nominations for The Best FIFA men's player award, with the 34-year-old having led Madrid to last season's LaLiga title.