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The Denmark international was on the receiving end of a strong challenge from Reading striker Andy Carroll during Manchester United's 3-1 FA Cup fourth-round victory.
Carroll avoided punishment from referee Darren England for the tackle, though he was later sent off for two bookable offences.
Eriksen's injury is a cause of concern for United, with crucial Premier League clashes and a Europa League showdown with Barcelona on the horizon, and ten Hag is waiting for a full assessment on the problem.
"It's always difficult to say so soon after the game finished but it's an ankle [injury] and we have to see what the diagnosis is," he told a post-match press conference.
"It will be a minimum of 24 hours before we know that, and then I can say more."
ℹ️ Injury update on @ChrisEriksen8. #MUFC || #FACup— Manchester United (@ManUtd) January 29, 2023
Victory for United keeps the club in contention across all competitions this season and the performance of Antony caught the eye, having provided the assist for Casemiro's opener.
Ten Hag had called for more from the pre-season signing after the midweek EFL Cup win against Nottingham Forest and, while he has seen progress, feels there is still more to come.
"I have some experience with him. We have to challenge him and if you challenge him he can adapt, adjust his game, that is what we have to do, definitely," he said.
"He has to be more variable, more dynamic, but also he needs his team-mates and his team-mates around him. But also [needs to know] how to use your team-mates.
"He has to work on that but he is investing in that at the moment and you see the progress.
"But still I think there is a lot of room for improvement."