Fighter Leah McCourt said Curtis, 31, had sustained “a broken back, a broken neck and a dislocated spine”.
Curtis has been a professional since 2015 and has fought on Cage Warriors and Bellator cards.
McGregor posted on social media that he was “sending my support and well wishes” to the Dublin fighter.
Belfast boxer Michael Conlan, MMA fighters Molly McCann and Dillon Danis and coach John Kavanagh have also donated to Curtis and his family.
In a post on Instagram, Belfast’s McCourt said “there is no exact end date as to when his treatment will be complete”.
“Ryan will never be able to do what he loves, and fight or train in MMA again. A sport he has dedicated his life to from the age of 11,” she added.
“Ryan has the most infectious positive outlook in life and has been through some of the most horrific circumstances, always coming out a better human, man and friend.
“He is still showing his positive outlook, his determination and mindset to overcome yet another challenge that life has presented.”
Curtis’ partner, Emma, posted on social media that she was “overwhelmed by the tremendous kindness”.
“The love and support for Ryan are truly a testament to his remarkable character. Ryan remains optimistic, I have never known anyone with a stronger mindset than him.
“I truly believe that Ryan will hug me and our beautiful daughter Kassia again. Please keep Ryan in your prayers.”
‘Such a special guy, a massive character’
“Ryan can light up every room he walks into, he is one of those guys that you’d usually hear him before you see him, and I mean that in the very best way. He really is such a special guy, and such a massive character.”
“He is a fantastic athlete, and such a dedicated athlete. He travelled crazy hours every day just to train, and has dedicated his life to his craft from a very young age.
“As a team, as a community, and as a sport as a whole, we’re absolutely gutted that something like this has happened, to not only a great young athlete, but a young father with a very young family.” https://mantrasungokong.com/
“It says a lot about Ryan when you see the entire MMA community come together the way it has. To show their support, and to help raise the funds they have that can hopefully take care of anything that’s needed, and ease the pressure on their young family.”