Aaron Hernandez Victim -- PUNCHED AND STRUCK REPEATEDLY ... Lawyer Says

The jail inmate who was attacked by Aaron Hernandez does NOT want to testify against the NFL star because he doesn't want to "be a rat" ... this according to the victim's lawyer.

TMZ Sports broke the story ... Aaron pummeled a fellow inmate back in February after a verbal dispute -- and now the victim's lawyer has ID'd the guy as 25-year-old Andrew Booker.

FYI -- Booker was arrested by a police gang unit back in in September with 16 bags of coke and a loaded gun in his waistband.

Hernandez was charged with assault and battery for the incident -- but Booker's attorney Michael Maloney tells The Sun Chronicle he doesn't want to testify against him.

"He doesn’t want to go after Hernandez. He doesn't want to be a rat,” Maloney says.

Maloney also said the fight started just like we said it did in our initial report -- "They were having a verbal feud. It escalated, got out of control and Booker was assaulted while handcuffed."

Maloney says Booker was punched and struck repeatedly ... and suffered cuts, bruises and scrapes.

Booker is now considering taking legal action against the Bristol County Sheriff's Department -- "He’s really disturbed he was allowed to be put in that situation."