United had hoped to offload Pereira on a permanent basis after agreeing a fee with the Brazilian club, but a U-turn has thrown the deal into jeopardy.
Officials at Flamengo are now pushing to stop the transfer from happening all together, with the midfielder's recent poor form while on loan not helping his case.
However, Brazilian media sources state 'important people on the red and black board are working behind the scenes' to prevent the agreement being finalised.
Although United and Paulo Sousa 's side have reached a 'verbal agreement', president Rodolfo Landim is being persuaded to give up on the signing and address more pressing positions with their limited funds.
Pereira's contract at Old Trafford expiries in less than 18 months, putting his Flamengo off paying £8.7million for his signature.
The Rio de Janeiro giants already wrangled his asking price down during the January transfer window after an option to buy for more than double (£16.6m) was inserted into his season-long loan deal back in August.
The permanent transfer was expected to be announced after their Super Cup clash with Atletico Mineiro on Sunday, but it appears the 26-year-old's future remains undecided.
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