The 26-year-old slipped down the pecking order at Old Trafford under Ole Gunnar Solskjaer and was loaned to Lazio for 2020-21 before heading to the Brazilian top flight.
Pereira has quickly become a regular for Flamengo and has made 49 appearances for the Serie A side in all tournaments, scoring seven goals and providing three assists in the process.
The midfielder has endured a tougher time of things in 2022 with Flamengo, though, which has led to doubts over the prospect of a permanent deal.
Flamengo are understood to possess the option to sign Pereira for a fee of €10.5m (£8.9m), but as things stand the former PSV Eindhoven youngster will be back at Old Trafford next month.
However, Junior is determined to strike a permanent deal for Pereira, claiming that players with his "growth potential" are "scarce" in Brazil at present.
"It's just an opinion. I hope he stays. Players of this level, players with this potential, are few in Brazil. I have no doubt that this boy can still grow a lot, he can evolve a lot," Junior told reporters, as quoted by the Manchester Evening News.
"How will it happen? I don't know, but it would be really nice if we could hold onto this kid because he has a lot of qualities. He is a player that draws attention in any way. He has growth potential, players of that level are scarce at the moment within this country."
Pereira has scored two goals and set up two more in 25 appearances for Flamengo in the 2022 season so far, and his contract at Man United will expire in 12 months' time.
The one-cap Brazil international has been with Man United for over 10 years but has only made 75 senior appearances in that time, scoring four goals and providing five assists.
Pereira has won one piece of major silverware at Old Trafford in the form of the 2015-16 FA Cup, while he became Under-21 Premier League champion in 2013, 2015 and 2016.
New manager Erik ten Hag could yet hand Pereira a lifeline in Manchester if Flamengo decide against a permanent deal, but the club are still said to be open to selling the midfielder for the right price.
Ten Hag has already waved goodbye to numerous players ahead of his first season in charge, with Edinson Cavani, Lee Grant, Juan Mata, Jesse Lingard, Nemanja Matic and Paul Pogba all heading out of the exit door.
The Red Devils missed out on the signature of Darwin Nunez to Liverpool but are still pressing to sign Frenkie de Jong from Barcelona, and negotiations for the Dutchman have supposedly reached an advanced stage.
Man United are yet to announce any new arrivals this summer, and former right-back Gary Neville recently claimed that he was "worried" by his side's lack of early activity.