That colossal impact on the popular tourist attraction was revealed this week by Emma, the Duchess of Rutland, who lives there with her family.
She was speaking as some social distancing restrictions begin to be relaxed with schools and shops reopening but confirmed there were no immediate plans to reopen the castle to the public until the safety of visitors and staff can be guaranteed.
Businesses remain temporarily closed at The Engine Yard retail park, which was opened to great fanfare by Hollywood star Liz Hurley nearly two years ago, although The Fuel Tank cafe and restaurant is selling takeaway food from Thursday to Saturday.
The castle grounds were also due to host a range of public events, including a VE Day concert last month, jousting tournaments this month and a large flower and garden show next month.
They have been lost to the pandemic restrictions and a new feature - Royal Afternoon Tea followed by a tour of the castle to see where scenes for Netflix blockbuster The Crown were filmed - was also expected to be very popular.
The Duchess told the Melton Times: “We are going to play it by ear for now in terms of opening everything up again.
“I just want it to be safe and I want to do the right thing for people who visit and for the businesses at the retail park.
“We have lost about £2.5million worth of business as a result of the closures and summer events being cancelled.
“We don’t know at this stage when we can begin opening again to the public and we will wait for the government advice.”
One positive for the estate is the reopening of the 16-acre garden landscape to the public, with free access at weekends from the last week in May.
Charges will be brought in again from this weekend and visitors are advised to pre-book their tickets online at www.belvoircastle.com/product/tickets-for-garden-entry-may/ with children 15 and under getting in free if with an adult.
The gardens were designed and landscaped by the 5th Duchess of Rutland, Elizabeth Howard, and were regarded as one of the greatest gardens north of London in the 18th century.
Over the years, the gardens have been lovingly cared for with several Duchesses leaving their own mark.
The 11th Duchess says she is determined to continue redeveloping these beautiful gardens to restore them to their former glory.
She said: “We opened the gardens free of charge to start with because I wanted people to get the chance to come to a lovely open space and stretch their legs.
“It has been absolutely packed with long lines of traffic stretching back to Woolthorpe, queuing to see the gardens.”
The Duchess added: “Whilst visitors have been absent from Belvoir, the gardens have burst into life with narcissus, camellias, rhododendrons and magnolias.
“They all look spectacular at the moment and we hope that a walk in the outdoors will be a welcome relief from the stresses of recent times.”