The 28-year-old’s injury will prove a sizeable setback to boss Jose Mourinho, with United still chasing the Europa League title and battling for a top-four Premier League berth.
Mata’s blow is the latest concern for United, following quickly on from Mourinho confirming “long-term injuries” to defenders Chris Smalling and Phil Jones.
United confirmed Mata’s injury in a short statement last night, saying: “Juan has had surgery for a groin injury. Further updates on his recovery will follow in due course.”
Allied to the new injuries for Smalling and Jones, United must also do without Paul Pogba, Ander Herrera and Zlatan Ibrahimovic for today’s Premier League clash at home to West Brom.
Herrera and Ibrahimovic will miss the West Brom encounter through suspension, with Pogba sidelined due to hamstring trouble.
Defender Jones withdrew from England’s squad last week owing to a toe complaint that appeared to have been sustained in a training ground clash with United team-mate Smalling.
Smalling also withdrew from England’s squad days later, and has been spotted with his right leg in a brace.
So just when Mourinho would be aiming to kick United’s season into top gear, now the Portuguese boss must juggle his resources to offset the loss of a clutch of influential regulars.
When confirming the injury lay-offs for Smalling and Jones yesterday, Mourinho insisted United must not dwell on their mounting problems.
“We cannot be here crying or speaking about the players who are not available to play,” said Mourinho.
“You know Zlatan and Herrera are suspended, you know that Herrera is two matches banned for that episode against Chelsea.
“You know what happened in the English national team with Smalling and Jones.
“You know that we have also Pogba injured, but I repeat they’re not important.
“The important players are the ones that are ready to play and the ones I trust and the ones who are going to give us everything tomorrow to try to keep us in the fight for the top four.”
Mourinho, meanwhile, has insisted he has no interest in signing anyone whose desire to play for United is tempered by concerns over location and weather.
Mourinho has given executive vice-chairman Ed Woodward “difficult” but realistic targets, with the manager sure they will “do something interesting” to improve the squad as talk over a summer move for Atletico Madrid’s Antoine Griezmann persists.
The France international has previously spoken about concerns over English weather and Mourinho gave short shift to suggestions that the allure of other cities could influence targets.
“If a player wants to move to London, enjoy London — we don’t want you,” Mourinho said. “If the first thing you think is where you’re going to live, well, think Los Angeles.
“Galaxy would be the first choice and then Vitoria Setubal, go to the beach every day. There are beautiful places to live and to play.”