Two of the holding companies behind Four Seasons Health Care appointed administrators today.
The group serves about 17,000 residents and patients and employs some 20,000 staff.
It operates Layden Court Care Home in Maltby and Balmoral Care Home in Woodhouse.
However, Four Seasons said the move would not affect care arrangements or lead to the closure of homes.
Group medical director Dr Claire Royston is quoted in national press as saying: “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.
"It marks the latest stage in the group's restructuring process and allows us to move ahead with an orderly, independent sales process."
The GMB union said the government needed to step in urgently to reassure Four Seasons staff and residents.
Rehana Azam, GMB national secretary, said this was evidence that “our care system is in crisis” and is “crumbling beneath us because the funding isn't there."
Four Seasons said it had appointed professional services firm Alvarez & Marsal (A&M) to handle the administration.
While the holding companies - Elli Finance (UK) and Elli Investments - are in administration, the operating companies that run Four Season homes are not.
It is understood the group said it had secured funding to ensure continuity of care while it seeks a new owner.