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McIlroy has indicated that conflicting loyalties make him uncomfortable with declaring to be part of either a Great Britain or Ireland team for the Games.
The 27-year-old, born in Northern Ireland, opted to represent Ireland, before pulling out of Rio 2016 because of concerns about the Zika virus.
"More likely than not I won't be going to the Games because of my personal feelings." said the world number two.
McIlroy says it is a decision he has not taken lightly, one that "I have fought with myself over for so many years".
"The Olympic Games are fantastic and I think golf's inclusion is fantastic, but for me its something I don't want to get into. That's a personal choice and hopefully people respect that decision.
"It went well in 2016 and I hope it goes even better in 2020 but I probably won't be a part of it.
"If it upsets some people that's ok, I can't please everyone  but as long as I am true to myself I'll be happy."
McIlroy will take part in his first tournament of the season, the South African Open, this week.
Rory McIlroy says he will probably not compete at the 2020 Olympics in Tokyo.