The incident was reported to Lincolnshire Police at 5.10pm yesterday (6th March) and is thought to have taken place just prior to this time at around 5pm.
The 36-year-old male victim was taken to Hull Royal Infirmary hospital with serious injuries including what is thought to be a stab wound to his back.
He is currently in a medically induced coma but is described as stable.
This video shows the area where the attack may have happened.
The attack may have taken place on Ropery Road although the police are also considering the river bank, which runs parallel to the road as a potential scene of the crime.
This is an area frequently used, especially by dog walkers and it could be that someone has seen the attack and police officers are urging anyone in the area at the time to come forward and give details of what they know.
If you saw the attack, or have any information in relation to it, please call 101 with incident reference number 300 of 6th March.
A 36-year-old man and a 30-year-old woman have been arrested in relation to the incident and are currently assisting police with enquiries.