The Spaniard enjoyed two successful seasons at Chelsea after being brought to Stamford Bridge by Andre Villas-Boas.
But Mata fell out of favour under Jose Mourinho this campaign and all parties had decided that a fresh start would be beneficial for everyone involved.
And so the 25-year-old started anew at Man United, getting off the mark with two assists a couple of games into his Old Trafford career. All was good in the world again, while belief in David Moyes and the Glazers had been temporarily restored.
Yet after just seven games in a Manchester United shirt, it's back to square one for the Spaniard. Known for his ability as a central attacking midfielder, Mata has been shifted out onto the left wing by Moyes and is yet to scored for United.
And his ineffectual performance against Liverpool has provoked a serial response across the footballing world.
"United have always had fantastic wingers but Mata is not a winger and you make yourself look worse by playing him there. He needs to play in that No 10 position but how do you sacrifice a man you’re paying £300,000 a week?" Jamie Redknapp wrote in the Daily Mail on Sunday night.
Redknapp, however, is not the only one, with fans from across the Premier League taking to Twitter to ask just what the point of Mata's move to Man United was.
Once heralded as a potential season-changer, the 25-year-old's decision to join United is now the subject of ridicule. Will the Spaniard prove his critics wrong?
Just a thought, is Juan Mata at £38m, the worst signing of the season? How long before he is declared a flop? #MCFC # MUFC— Stephen Bridge (@SteveJBridge) March 16, 2014
I’m a big fan of Juan Mata, but you don’t spend £37m on a player and play him out of position.— Prince H (@PrinceHusso) March 17, 2014
I feel for Juan Mata. Nice guy who was forced to make a wrong move. He would have got better places to go had he waited. No doubt in class.— Vinu George (@vinugeorge) March 17, 2014
Juan Mata has added nothing to United. Along with Ozil he was considered one of the best until they both transferred for more money— Ollieeee (@OliverHall97) March 16, 2014
Giving Juan Mata to Moyes is like giving Beyonce to Justin Beiber - not a clue what to do!— Mr B (@Dj_Mister_B) March 16, 2014
The biggest question has gotta be - why buy Juan Mata for £37m and play him on the wing #headsgone— Lewis (@LM0161) March 16, 2014
Bet Juan Mata wishes he'd joined a big club afterall.— Al O'Pecia (@happydobbin44) March 16, 2014
Was Mata right to leave Chelsea for Manchester United?