Hernandez was brought to St. Luke's Hospital in New Bedford Saturday and was back at the Bristol County jail in Dartmouth about an hour later, Bristol County Sheriff Thomas Hodgson said Sunday.
Hodgson said he can't disclose what happened because of medical privacy laws.
Hernandez, a Bristol, Connecticut, native, has pleaded not guilty to murder charges in connection with the killings of two men in Boston in 2012 and the killing of another man found near Hernandez's home in North Attleborough, Massachusetts.
The hospital visit, first reported by WBZ-TV in Boston, came a day after his attorneys said in a transfer request that Hernandez should be moved to a jail closer to Boston because communication with his attorneys and his personal safety are being compromised.
Boston-based attorneys Michael Fee and James Sultan complained their client has dealt with "bizarre and unprecedented" restrictions in his communications with his lawyers. Hernandez cannot always speak privately over the phone and in-person visits are limited to a specially-designated visitation room at the prison, they said.
The lawyers also suggested Hernandez's safety is at risk now that he faces criminal charges for allegedly threatening to kill a prison guard and his family, and in an alleged jail altercation with another inmate. Hernandez has pleaded not guilty.
Hernandez is set to appear in court in Boston this week in the 2012 drive-by shooting that killed Daniel de Abreu and Safiro Furtado.
Hernandez has pleaded not guilty to all three killings.