Platini has made it clear he would not vote for Turkey to host the tournament if Istanbul wins the contest to stage the Olympics.
Istanbul's Olympic chances have soared after the IOC shortlisted the city along with Tokyo and Madrid - and rejected Doha and Baku.
Many Olympic watchers rate Istanbul now as clear favourites - it would be the first city from a predominantly Muslim country to host the Games.
The three Celtic nations have made a formal expression of interest in bidding to host Euro 2020 and Platini's declaration should increase the chance of a bid.
Platini, in Budapest for the FIFA Congress, had backed Turkey for 2020 publicly but said in an interview: "If Turkey is given the Olympic Games, they will not have the Euros. If they don't get the Olympics and they still bid for Euros I will still vote for them.
"The two decisions are not at the same moment. They can carry on bidding for both if they want - I'm not particularly happy about that but it's their problem not mine - but if they get the Games they won't be in Euros. They can gain everything or lose everything."
Further talks about a possible bid have taken place between officials from the Scottish, Irish and Welsh FAs here in Budapest but no decision will be made for some months.
The decision of the IOC executive board to shortlist Istanbul does make a bid by the Celtic nations more likely, and Platini's comments will also be an encouragement.
Other UEFA figures remain sceptical of Turkey's bid for Euro 2020 due to the match-fixing crisis that has caused chaos in the country's football administration.
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