Everton fear Jack Grealish may need surgery to repair a stress fracture in his foot and could miss the rest of the season.
The 30-year-old has been to see a specialist this week, having reported for treatment at Finch Farm, the club's training base, on Monday for what was assumed to be a calf problem. After further investigations, it emerged the issue was significantly more serious.
David Moyes, Everton's manager, has not given any guidance on how long he will be without Grealish but if an operation is required to rectify the damage, there is every possibility his campaign would be over and that would be a huge blow for both him and his current club.
A significant lay-off would effectively extinguish Grealish's last lingering hopes of making Thomas Tuchel's World Cup squad, while it would rob Everton of their most creative talent at a time when they are hoping to mount a challenge for Europe.
Asked whether a procedure might be necessary, Moyes confirmed: 'That's part of the discussion to be made with the surgeon. Obviously we are not going to get good news, but there are no dates I want to give out at the moment. We are waiting on a couple of things coming back.
'It is a blow to lose him. He didn't come in [complaining] about his foot. He had a kick on the calf and we thought he'd be OK. That it was just a kick on the back of the calf and he would be OK in a couple of days but they checked his foot out and he has a stress fracture.
'It's a real pity for the boy. He's been back at it, enjoying it and doing what he is good at. He has been supported brilliantly by the supporters at Everton. They think so much of him and it's just disappointing he is going to have some time off.'
It would also call into question whether Grealish will play for Everton again – his loan from Manchester City expires at the end of the current campaign and discussions between the clubs over a permanent deal have yet to take place.
Grealish has thrived in the environment Moyes has created and while he received a ticking off from him last week, following a petulant red card in a 1-1 draw with Wolves, the relationship between the pair has been outstanding. His absence may force Moyes to move in the transfer window.
'We're not thinking about (his future) at the moment,' said Moyes. 'We are only thinking about Jack – we are upset for him and disappointed he has got an injury.
'We are in close contact with Manchester City so we will see how that works as we go along and get more decisions from the specialist.
'It will add to our thinking (about signing someone), that's for sure. Getting them is a different story but it will add to our thinking of is there anything out there we can consider.
'But, at the moment, we are just waiting to get the assessment back from the specialist and then we'll know more.'