Gary Reed, 46, says he was struck on the head with a metal dumbbell bar in the gym in Pattaya on May 17.
He said he could have been blinded and had to have 60 stitches to repair damage around his eye.
He added he suffered a fractured right eye socket and retinal bleeding.
Gary has already paid almost £600 in medical fees and been told he needs further surgery.
His friend Andrew Neeson said: “Gary wants to get home to see his two young daughters, but can't fly until funds are raised, as he can't fly until he has treatment.”
Gary’s sister Julie Stafford has set up a Gofundme page to raise £15,000, with more than £2,700 being raised so far.
She said: “My brother was attacked in a gym in Thailand. He’s not allowed to fly back to get surgery and if he doesn’t get it he will lose his eye and sight. They’re charging him £15,000 for the surgery.”
Gary said: “I have had my orbital bone broken and received dozens of stitches. I need urgent surgery and the cost is more than £15,000. I'm lucky my sister has set up a Gofundme page to help with the cost.
"Unfortunately my health insurance ran out recently and as I was returning home on June 1, I didn't renew it. My operation will be in two weeks provided I can raise the funds.”
The Gofundme page is at https://www.gofundme.com/f/to-help-save-my-brothers-eye-sight