Conor McGregor has claimed that he held talks about buying a stake in Celtic from their principal shareholder Dermot Desmond.
McGregor, who has previously been pictured in a Celtic shirt that was given to him by the side's former defender Kieran Tierney, made the revelation when responding to a question on Twitter.
He wrote: "A conversation came up regarding Celtic first to be honest. To acquire shares from Dermot Desmond.
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"I am certainly interested in acquiring a sports team at some stage! Both Celtic and Man United are teams I like for sure.
"But I am open. I feel I could do big things for a club."
Desmond first invested in Celtic in the 1990s, and said in March that his shares were not for sale.
The Irish businessman and financier previously held shares in Manchester United, before the club was acquired by the Glazer family.
McGregor has also stated his interest in buying the Premier League club, tweeting last month: "Hey guys, I'm thinking about buying Manchester United! What do you think?"
Last month, Forbes ranked United fourth on its list of the world's most valuable football clubs, with a total valuation of $4.2bn (£2.98bn).
McGregor is one of the biggest stars in UFC and returned to the octagon in January against Dustin Poirier after a year away.
The Irishman was beaten on that occasion, but will have a chance to avenge his loss when the two men meet for a third time in Las Vegas in July.
McGregor has also previously ventured into boxing, with Forbes estimating he earned around $85m from his 2017 defeat to Floyd Mayweather.
Celtic 'working hard' to appoint new manager
Celtic have assured fans they are planning to return to the top of Scottish football in the "shortest possible timeframe", and are working hard to appoint a new manager.
Former Bournemouth boss Eddie Howe remains the frontrunner but the Celtic support are growing increasingly anxious the longer the wait goes on.
The fallen champions saw their dreams of 10-in-a-row collapse as Rangers wrestled back the crown after a decade in their Old Firm rivals' shadow.
"The club is working hard to complete the appointment of the new Celtic manager and relevant football staff and will be doing all we can to confirm this as soon as possible to our supporters," said a statement.
"Rightly, there will always be a huge appetite for information from our supporters. Unfortunately, we are not able to make regular public comment on this matter, but we fully understand and appreciate the need to complete this process as soon as we can.
"We also acknowledge and understand the frustration of our supporters during this process, but our objective of course is to ensure that we secure the best candidate possible to take the club forward and this is our focus.
"We will update all our supporters through our club communications channels as soon as we are able to.