The company has appointed corporate undertakers at Alvarez & Marsal (A&M) to carry out the process following an aborted sale attempt.
Four Seasons houses 22,000 elderly residents across 322 homes, although the firm insists that operations will be unaffected by the move.
“The operating companies under which the care home and hospital operations sit are not in administration and continue to be run as normal by the existing leadership teams,” Four Seasons said.
The collapse is the biggest care homes failure since Southern Cross collapsed in 2011.
Only weeks ago, Four Seasons insisted that it had “sufficient operating liquidity” to be able to complete the sale process.
Dr Claire Royston, group medical director of Four Seasons, said: “Today’s news does not change the way we operate or how our homes are run or prompt any change for residents, families, employees and indeed suppliers.
“Our priority remains to deliver consistently good care. It marks the latest stage in the group’s restructuring process and allows us to move ahead with an orderly, independent sales process.”
Terra Firma Capital Partners, the private equity firm led by Guy Hands, bought the group in 2012 for £825m but has since seen a £450m writedown on its investment.
It has also ceded control of the group to US hedge fund H/2 Capital Partners, which holds a large amount of its debt.
It has been hit by a cut in local authority fees, increased costs, the introduction of the national living wage, and the group has continuously cautioned over its long-term stability.
Richard Fleming, of A&M, said: “We are committed to ensuring the group delivers continuity of care as we work to undertake the independent sales process.
“The group has continued to improve its quality ratings across their portfolio of homes and hospitals.
“The group’s operations are fundamentally strong and a successful sales process will enhance those operations’ ability to thrive.”
The CQC said it was “fully aware of today’s developments and will continue to closely monitor the position.
“Our market oversight regulatory responsibility is to advise local authorities if we believe that there will be likely service cessation as a result of likely business failure. We do not believe this to be the case at this time.
“We will continue to keep this under review and remain in regular contact with Four Seasons Health Care throughout this process.”