Lisandro Martinez left Old Trafford on crutches and in a protective boot in worrying scenes for Manchester United fans.
The instrumental defender, 25, went down with nobody near him late on in the dramatic 2-2 draw with Sevilla in the Europa League quarter-final.
He pulled up and gripped the back of his ankle as he broke down in tears.
Two Sevilla players – Martinez’s Argentina team-mates Marcos Acuna and Gonzalo Montiel – carried him off the pitch before a stretcher took him away.
But pictures from behind the scenes at the Theatre of Dreams showed the centre-back in his United coat using crutches and his right foot in the big boot.
Erik ten Hag ruled out an Achilles injury, which would have been devastating for both the player and the club.
But TyC Sports reporter Gaston Edul in Argentina suggested it could be a fifth metatarsal injury, with more tests expected today.
Ten Hag, though, confirmed he is almost certain to be without his World Cup-winning defender Martinez for Sunday’s trip to Nottingham Forest.
The Dutchman said: “No, it is not the area. But I can’t tell what it is. But it is not the area of Achilles.
“We have very good replacements with Harry Maguire, Victor Lindelof, Luke Shaw, so we have players who can replace them. But of course, it is a miss.
“I think he will not play on Sunday. It looks like that but I can’t say what is the diagnosis and I prefer to wait and then we are clear and we know exactly what it is.
“I have spoken with him, he is okay, he is calm. Of course and we compete in three competitions and then you need a squad.
“So if Licha Martinez, Raphael Varane are not available on Sunday then others have to do it.
“We have seen on Saturday Harry Maguire played a good game and he came in tonight and also played a good game.
“I have an idea what we can play on Sunday but first we have to see tomorrow and talk with the medical team, see who came out of the game and then we have a plan and then we will bring a good team on pitch.”
The injury blow could be worsened if United are without Martinez for the second leg in Spain next week – with Varane and Marcus Rashford doubts plus Bruno Fernandes is suspended following a harsh yellow card.
2Lisandro Martinez went down clutching the back of his ankle against SevillaCredit: Richard Pelham / The Sun
2The Argentine looked devastated as he was carried off on a stretcherCredit: Richard Pelham / The Sun
