Cleveland Police are today faced with the mystery of how a man came to be found on the A66 with serious injuries to his groin area.
A 22-year-old man has been arrested on suspicion of assault and is currently in police custody.
Police were alerted to an incident on the A66 at 4.50am this morning following a concern for safety.
Police took reports of a man in a distressed state on the carriageway.
Police who arrived at the scene immediately located a man with serious injuries who required hospital treatment who they believe to be aged 40 and from the South Bank area of Middlesbrough.
Police closed sections of the A66 from Greystones Roundabout to Church Lane in order to carry out an investigation which has now been lifted following forensic examinations.
Anyone with information which may help the investigation is asked to contact police on the non-emergency number 101.