"When I saw the specialist, he explained the situation and told me my spine was under pressure," Hayles told the club's official website.
"He said I had to have treatment to make sure I could do things like walk in future.
"I was originally aiming to be back for pre-season in late June but I'm back now. I hope to make it back for two or three first-team games before the end of the season.
"The neck will always be stiff but just something that'll have to be treated along the way now. It won't hold me back."