The 31-year-old, after becoming the club’s all time top goalscorer earlier this year, joined up with his boyhood club on a free transfer back in July.
He has already claimed two goals for the Toffees against Stoke and Manchester City so far this season and will make a return to Old Trafford on Sunday.
Writing in his weekly blog, Mata noted that seeing Rooney wearing a different shirt and playing as a visitor at the Theatre of Dreams will be strange to say the least.
“I hope Old Trafford will welcome him as he deserves. It will be weird to see Wayne playing with a different shirt, to be honest, but this is the decision he made last summer and we wish him the best of luck.”
There is something about Rooney wearing an Everton shirt that is deeply unsettling – almost unheimlich, like a feeling of simultaneous familiarity and discord.
And seeing him grace the Old Trafford turf will only heighten that very notion. Phil Jones and Eric Bailly have already confidently frozen out one striker on their return to United in the form of Javier Hernandez, but Rooney presents an entirely different challenge.
He may be deficient on a technical and physical level, but make no mistake: no other rival player knows this team – their frailties, their strengths, their methods – better than Rooney, and Mourinho ought to be careful.