Reports from Catalonian media revealed that Barca have fallen behind the Red Devils in striking a deal for the Frenchman, and United could complete the transfer in the first few days of January, making him their first signing of the Ralf Rangnick era.
Kamara has established himself as a regular in the Marseille team this season with 15 appearances across all competitions, scoring once in a 4-1 win over Lorient in October.
A big selling point in Kamara's favour is that his contract at the Stade Velodrome expires in June 2022, leaving him free to talk to other clubs next month.
Kamara further fuelled speculation of an imminent departure from the French club after turning down a two-year contract extension offer in September.
United will have to make do with their existing options in central midfield for now, with the club next scheduled to face Newcastle United on 27th December.