The man found with a head injury on Belmont Street on Monday is still in hospital, in a serious but stable condition, police said.
As previously reported, the 41-year-old man was found injured on the street in Lincoln on June 2 at around 3.45pm.
On Wednesday morning, Lincolnshire Police said he is still being treated for the injury to his head at Lincoln County Hospital.
Officers also arrested three men aged 20, 22 and 25 on suspicion of hurting the 41-year-old.
They have since been released on bail pending further enquiries.
Detectives would like to hear from anyone who may have seen or heard any disturbance in the Belmont Street area around the time, or who saw the injured man.
Anyone with any information related to this incident is asked to contact Lincolnshire Police on 101 quoting incident 326 of 02/06/2014.
Alternatively they can contact the independent charity Crimestoppers anonymously on 0800 555 111.