The incident took place in Ingram Road, near to the junction of Shaw Road, at about 9.45pm yesterday (Monday, April 29).
A spokesman for Lincolnshire Police said: “The victim is currently in hospital in a critical condition. Police are appealing for any witnesses that were in this area around this time to make contact with the investigators, quoting incident 461 29/04. They are also interest in anyone who may have travelled through this area with a dash cam in their vehicle.”
In an earlier statement, police said a man in his 40s was taken to Queen’s Medical Centre, in Nottingham, as a result of the incident.
A scene guard is in place while investigations continue, they added.