Jesse Lingard was forced off late on during West Ham's Premier League loss to Newcastle United on Saturday afternoon, leaving both David Moyes and Gareth Southgate sweating over the England international's fitness.
The playmaker, on loan from Manchester United, scored a second-half penalty in a thrilling five-goal encounter at St James' Park that saw David Moyes' side handed a major blow in their quest to secure an unlikely Champions League berth next season.
Lingard, whose tally of nine goals for the Hammers since his arrival in the new year represents the best full-season figures of his club career, is in the form of his life right now, but had to be assisted in leaving the field amid fears that he could be set for a disruptive lay-off.
What happened to Lingard?
Having drawn the Hammers level at 2-2 with a spot-kick from a VAR-assisted penalty call, Lingard was unable to prevent substitute Joe Willock from putting Newcastle back into the lead shortly afterwards.
With the game restarted, the midfielder laid down on the turf, near the centre-circle during a pause in play, clutching at his leg in some discomfort.
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After a brief discussion with staff on the sidelines, Lingard exited the field, assisted by a club medic, as Moyes replaced him with Manuel Lanzini.
What could the injury be?
It is too early to know whether Lingard, who became the first West Ham player to score in five consecutive Premier League games since Diafra Sakho in 2014, was merely removed as a precaution or if his exit is reason for genuine concerns about his long-term fitness.
Suggestions are that Lingard could have picked up a hamstring problem, though the severity of any such blow would still take time to fully assess.
What does this mean?
If Lingard is set for a spell on the sidelines, it would hand both West Ham and England headaches ahead of a crucial few months for both.
The Hammers' defeat to Newcastle opens up the door for both Chelsea and Liverpool behind them to leapfrog them into the top four, leaving their Champions League ambitions hanging precariously in the balance.
Lingard is naturally viewed as an essential cog to any successful charge, given the impact he has had since arriving at London Stadium, and any lay-off may well prove a major blow to his side's hopes of a European qualifying finish, including the Europa League and Europa Conference League.
As for the Three Lions, Lingard's prowess during his recall for the March international break suggested a player who had firmly drawn themselves back into Gareth Southgate's plans for Euro 2020 - but with the manager having stressed he will pick only players at full fitness, there could be a race against time now to make the cut.