Over 1,900 jobs are to be cut under plans revealed by the owners of Bella Italia, Cafe Rouge and Las Iguanas after calling in administrators.
The company said it would close 91 of its 250 restaurants, but that it has saved others for now.
It still leaves around 4,050 workers at the company's sites across the UK.
The board said that entering administration was in the best interest of stakeholders during the "extreme operating environment" it is having to trade through.
It is looking for a new owner, but said that the administration would allow it to end negotiations with landlords, a "critical step" before finding a buyer.
Chief executive James Spragg said: "After reviewing all our options with advisers, it became clear that we needed to take this action in order to protect the business and secure the best possible future for Casual Dining Group as we look to conclude a potential sale.
"We are acutely aware of our duty to all employees and recognise that this is an incredibly difficult time for them.
"Working alongside the administrators we will do everything we can to support them through this process with a view to preserving as much employment as we are able to."
Administrator Clare Kennedy, from Alix Partners, said: "We appreciate that this is an extremely difficult time for all those associated with Casual Dining Group.
"Our immediate priorities are to assist those whose employment has been affected by today's announcement and to secure a sale for the group in order to protect jobs and provide the Group's much-loved brands with a sustainable platform for the future."
