The Oak Street deals was CVS' third largest deal in the last decade and follows similar moves by rivals Walgreens Boots Alliance, Cigna Corp and UnitedHealth Group Inc as the focus on primary and urgent care delivery has increased since the COVID-19 pandemic.

Warren warned that consolidation may not lead to promised benefits, the report said.

CVS and Senator Warren's office were not immediately available to respond to Reuters' request for comment.

When the CVS-Oak Street deal was announced last month, the two companies expected to close it this year.

CVS' planned buyout of Signify Health, which provides home assessments mainly for patients enrolled in Medicare, has been under a lengthy antitrust review since its announcement in September.