The charity’s chairman Alistair Bow says since closing in March it has lost a staggering £350,000 - 90 per cent of its revenue - and has had to make 30 staff members redundant.
Despite having accessed Government help such as tax holidays and the job retention scheme Alistair says the centre has no prospect of any income.
Much of its income comes from school residential trips - which Public Health Guidelines advise against.
The chairman warns that - assuming the centre will be closed until Spring 2021 at the earliest – they will see a further 60 per cent decrease in revenue during the next financial year.
Alistair said: "We need some grant aid that will allow us to continue to look after the centre while closed and maintain what we have until we can operate again.
“We have now been closed since March with only 5 per cent of our budgeted income received to date.
“We now have a further six months of zero income forecasted as schools, groups and events are not booking or cancelling.”
Chairman Alistair, managing director at civil engineering and highways contractor Thomas Bow, fears without extra financial help the activity centre - established in 1938 - will be left to rot.
He said: “We can’t just shut up shop and leave the 250 acres to nature.
“More help is needed to help maintain this wonderful facility and help cover general costs like insurances, utility and basic maintenance costs - which cost around £150,000 a year.”
Alistair told how the centre contributed more than £3m to the local economy - paying £500,000 in wages and hosting up to 50,000 visitors per year.
He added that most visitors ‘usually head out into the local villages and towns to spend money’.
Guy Laurie, CEO of Walesby Forest, said although he understood the Government’s reasons for advising schools not to participate in residential trips there was no financial support for the maintenance of the buildings, activities, woodland and grassland.
He said: “When this crisis is over children and parents are going to want to go to a safe place and have some fun - something that has been in short supply in recent months.
“But unless there is direct financial support the activity centre industry will slowly disappear.
“I would like financial support in the form of grant aid and ideally the restrictions adjusted.”
Guy says that as outdoor activities for schoolchildren are currently carried out in bubbles Walesby Forest should be allowed to offer the same safety measures.
He said: “We can even offer accommodation in the same bubbles and limit our activities to those in the open air which reduce dramatically the risk of infection.
“We can work within the parameters schools can operate now but need the advice not to go on residential trips to be adjusted to a set of minimum requirements for centres to be able to welcome residential guests.
“Give activity centres a set of rules to work to and we will meet them."
After being contacted by the Guardian Sherwood MP Mark Spencer said: “I can assure the centre that I have raised their concerns with my ministerial colleagues.”