The husband and wife were at their home on Main Street, Torksey, at around 9.30pm on Wednesday, August 26, when three men entered the property via a rear door. They were armed with a knife-like weapon and their faces were covered.
The man, 60, tried to fight off the offenders and was attacked, suffering cuts to his head and hands.
He was taken to hospital for treatment. The woman, 64, was not injured in the incident.
The offenders escaped the property with a quantity of cash.
Det Insp Steve Knubley said: “This is a particularly nasty incident that has left the couple involved understandably shocked and distressed.
“We have been and continue to carry out a number of enquiries to identify those responsible.
“We are keen to hear from anyone locally who may have seen or heard anything unusual in the Main Street area around 9.30pm on August 26, or anyone who may have seen any men or vehicles in the area.
“We are grateful for any information, no matter how insignificant it might seem. It could be that piece of information that we need to help find these offenders.
“I would like to make clear how rare this type of offence is.
“We have a duty to make our local communities aware and ask them to remain vigilant and call us with any information they think might be relevant, but also ask that people don’t worry unduly.
“I appreciate this will cause concern to members of the public but I would like to reiterate that this is an incredibly unusual offence which we believe is a one-off and isolated.”
Det Insp Knubley also praised the couple’s bravery during the incident.
“The gentleman showed incredible courage in standing up to these intruders in his home and thankfully was not seriously hurt,” he said.
“We wish him a speedy and full recovery and will be working with the couple to ensure they have the support and help they need.”
West Lindsey District Councillor for Torksey, Coun Stuart Kinch, said: “This was very worrying to hear about.
“It has certainly made us be more aware of locking all doors to our property in an evening as we have three young children.”
Anyone with any information in relation to this incident is asked to contact Lincs Police on the non-emergency number 101 quoting incident 471 of August 26. Alternatively contact Crimestoppers anonymously on 0800 555 111.