PizzaExpress says it could shut around 67 of its UK restaurants, with uncertainty surrounding the future of its only Isle of Wight branch.
The move could put up to 1,100 jobs across the chain at risk.
It has recently put itself up for sale, blaming the "significantly more challenging environment" caused by the coronavirus pandemic.
PizzaExpress told Isle of Wight Radio it was too early to say which restaurants would close. The Island has one in Newport.
Highlighting the "current unprecedented backdrop" of COVID-19, bosses believe reducing the size of the business will help protect the majority of staff.
Andy Pellington, group chief finance officer, said:
"While we have had to make some very difficult decisions, none of which has been taken lightly, we are confident in the actions being taken to reduce the level of debt, create a more focused business and improve the operational performance, all of which puts us in a much stronger position.
"We can now plan to invest in both our UK&I and international businesses as well as support our teams as they return to work."
Zoe Bowley, UK and Ireland managing director, said:
"Our business has a long history of success, but the UK-wide lockdown has hit the hospitality industry particularly hard.
"While the financial restructuring is a positive step forward, at the same time we have had to make some really tough decisions.
"As a result, it is with a heavy heart that we expect to permanently close a proportion of our restaurants, losing valued team members in the process.
"As we continue to reopen our restaurants for dine-in and delivery, we will successfully navigate the extended period of social distancing expected in the months ahead and, in so doing, protect 9,000 jobs.
"The initial signs from the restaurants that have been reopened have been very encouraging and we hope that our loyal customers continue to support us now more than ever."
The company said it plans to launch a company voluntary arrangement (CVA) restructuring deal in the near future, which could lead to the closure of 15% of its 449 UK restaurants.
However, it insisted the final outcome had "yet to be decided".