The Irishman has helped the 'Hope for Evie' GoFundMe campaign, which has now raised over €100,000.
Evie has a rare genetic condition and she needs to travel to the US for specialist treatment.
A fundraiser at Crumlin Boxing Club raised €12,000 for the campaign, with a pair of gloves signed by McGregor selling for €500.
McGregor was then cheekily asked if he would match the €12,000 raised, to which Boxing coach Bra Brady said he replied: 'No problem'.
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Brady said, per Irish Mirror: He said: "We got €500 for the gloves and being a bit cheeky I asked if he would match whatever we made and he said it was no problem."
Evie was diagnosed earlier this year with a rare condition called microcephaly with pontine cerebellar hypoplasia, and a mutation in her CASK gene.
The serious condition stunts the development of the brain and can lead to a number of complications.
Irish doctors have little knowledge of the rare condition, but Evie's parents have found a neurological specialist in the US, enrolling their daughter on a four-week programme.
Evie's mum Emma said: “The time and effort put into the Crumlin boxing fundraiser was unbelievable and I would like to thank Katie, Sinead, Bra, Aaron and Phil and all involved in the club.
"They really went above and beyond on the day and we are forever grateful.
"It was not by any means a publicity stunt from Mcgregor as he did not even want it to be mentioned, we can’t thank Conor enough for helping our little girl.
"We cannot get over how much our little community has pulled together to help Evie reach her target, with hiting well over her target this now means Evie can go to Virgina for very intense treatment in Feb 2020.
"I would like to thank every person who has taking the time to donate to our baby girl."
You can donate to Evie's GoFundMe page by clicking HERE.News Now - Sport News