That's according to Sam Morgan of the Sun, with Spanish outlet Don Balon (h/t Morgan) reporting Mata "would welcome" the chance to return to his homeland.
The Spaniard was drafted in from Chelsea in January 2014 for £37.1 million, but after being moved around the team, he has sometimes struggled to replicate the excellent form he displayed at Stamford Bridge on a consistent basis.
Indeed, he has often been utilised out of the right flank—a position his lack of pace makes it difficult to shine in.
Samuel Luckhurst of the Manchester Evening News criticised him in December:
Formation not conducive and Herrera absence an issue but Mata has been in hiding again. Other #mufc attackers on the ball much more.— Samuel Luckhurst (@samuelluckhurst) December 5, 2015
The 27-year-old recently ended a lengthy goal drought in the 3-1 win over Derby County on Friday, per BBC Sport and ESPN Stats & Info:
Mata snaps a 14-match scoreless streak in all competitions https://t.co/2kAVGv4HEh— ESPN Stats & Info (@ESPNStatsInfo) January 29, 2016
Mata has six goals and seven assists to his name in all competitions this season and has created 45 goals in the Premier League since 2011.
His creativity and skill could see him work as a signing for Barca, and their indomitable front three would feed off his incisive passing, but the Blaugrana have little need for him with the likes of Andres Iniesta, Ivan Rakitic and Arda Turan already among those providing excellent service for their front line.
Further, as sports journalist Jonas Giaever shared in the summer, Mata seems to enjoy playing for United and explained as much in an interview with Marca:
Juan Mata has had a huge interview with Marca today. Reading it, you really get the feeling that he loves playing at Man United.— Jonas Giæver (@CheGiaevara) August 8, 2015
Juan Mata (to Marca): "This is what makes English football so special, and this club in particular."— Jonas Giæver (@CheGiaevara) August 8, 2015
The prospect of Barcelona signing Mata is undoubtedly one of the more outlandish deadline day rumours doing the rounds, as confirmed by Spanish football expert Guillem Balague:
Rubbish story of the day: the rumours about Mata. He is staying put, doesn't want to go, United don't want to sell at all— Guillem Balague (@GuillemBalague) February 1, 2016
The Catalan giants are also "desperately trying" to loan out Douglas before the window closes, with Marca reporting the club are "working round the clock" to find someone who will take him.
Douglas arrived at the Camp Nou in the summer of 2014 but has made just seven appearances for Barca, including two this season, with injuries taking their toll on the 25-year-old.
Indeed, the Brazilian has played so little that he has become a figure of fun, as Spanish football experts Sergi Dominguez and Rafael Hernandez demonstrate:
No. No one will take over Douglas' #16 shirt. The club have decided to retire the number. https://t.co/tUcN9wrZgl— Sergi Domínguez (@FutbolSergi) July 10, 2015
Douglas out for eight weeks, he will miss El Clásico. Huge blow for Barça.— Rafael Hernández (@RafaelH117) October 29, 2015
With so little game time under his belt and an unenviable injury record, Barca may struggle to find anyone willing to gamble on him, even on a loan deal.