Jack Grealish is expected to miss the rest of the season with a stress fracture in his foot, according to Everton boss David Moyes.
Grealish, on loan from Manchester City, is likely to undergo surgery on the injury, suffered in Everton's 1-0 win over Aston Villa on January 18.
Speaking ahead of Saturday's trip to Brighton, Moyes said on Friday: "We believe he's probably going to need surgery, but that's still not absolutely confirmed, but it probably rules him out for the rest of the season, yes.
"It's really disappointing for the player, and for the club, and all of us here. He's such an important part, he's a big character, big experience for us. We'll miss him. He's done a lot of really good things for us."
Asked if it was too early to think about Grealish's long-term future given his success at Everton prior to the injury, Moyes added: "Far too early".
The potential season-ending injury is a big blow for Grealish, who had hopes of breaking into England's squad for the World Cup this summer.
After a frustrating spell at City, Grealish had been thriving at Everton this term, with two goals and six assists in 22 appearances not telling the full story of the number of chances the 30-year-old has been creating.
Moyes said Everton continue to look for opportunities in the final weekend of the January transfer window, but indicated he is not expecting much, if any, business to happen.
"I'd like to say we're out there looking, which I think I've said in every press conference," he said. "We're out there looking. It's not that we're shying away from it. I would say it's probably less than likely than likely...
"(In) January you can find players, it's not to say you can't, but I think we're seeing this window becoming quite a difficult one for a lot of teams."
Meanwhile, defender Michael Keane returns to the Everton squad to face Brighton after a three-match suspension, while Kiernan Dewsbury-Hall and Jarrad Branthwaite both played 45 minutes on Monday as they stepped up their returns from injury.
Moyes said: "We've got Michael Keane back (from a three-match suspension), Jarrad Branthwaite made 45 minutes the other night and Kiernan (Dewsbury-Hall) back.
"We're still waiting a little bit on Charly Alcaraz (who was on the substitutes' bench against Leeds United) and Tim Iroegbunam (who wasn't, but was pictured in training this week), but they're all certainly getting much closer."
Analysis from Your Site News' Vinny O'Connor:
The news Evertonians didn't want to hear, and while David Moyes emphasised it's far too early to talk about what might happen in the summer, the facts of the matter are there's a chance Jack Grealish may have played his last game for Everton.
The admission from the Everton manager that Grealish is possibly facing surgery on the stress fracture in his foot, and that probably rules him out for the rest of the season, means that his loan spell will likely be over before he's ready for Premier League football again.
And Moyes again admitted the likelihood of bringing in reinforcements before Monday's deadline are slim. They are looking but in his words "it's probably less likely than likely".
He also didn't rule out departures, although you sensed any decision to let players go would not be at the detriment of his squad.
And it will be interesting to see whether or not Harrison Armstrong will be sent back on loan to Preston after making a favourable impression since his return. "He's not looked out place in the Premier League," the biggest compliment his manager could pay him.
Overall the squad is looking stronger with Jarrad Branthwaite and Kiernan Dewsbury-Hall making their returns as second-half substitutes against Leeds while Michael Keane is back from suspension this weekend.
Attention now turns to a potentially defining moment in their progression. Just over a year ago, Everton went to Brighton and won 1-0. Since then, a further nine away wins have followed in the Premier League - no one has won more on the road in that time.
Whereas last season Everton were desperate for points to beat the drop….this season Moyes is looking at a challenge for Europe as they sit just three points off sixth place.
January 31: Brighton (A) - Premier League, kick off 3pm
February 7: Fulham (A) - Premier League, kick off, 3pm
February 10: Bournemouth (H) - Premier League, kick off 7.30pm
Feberuary 23: Man Utd (H) - Premier League, kick off 8pm (live on Your Site)
Fabruary 28: Newcastle (A) - Premier League, kick off 3pm
