Frank Lampard has confirmed Everton right-back Nathan Patterson will be out for around six weeks with a medial knee ligament injury.
The Scotland international went off in the second half during the home defeat to Brighton & Hove Albion on Tuesday night, and boss Lampard said a scan has revealed the extent of the injury.
Ahead of Friday's FA Cup third round tie against Manchester United at Old Trafford, Lampard also said Anthony Gordon could return after missing the past two matches through illness, while he will weigh up Dominic Calvert-Lewin's availability as the striker's fitness is monitored following a recent comeback from a knee injury.
Lampard said: "Nathan's out for six weeks, unfortunately. It’s a medial ligament injury.
"It’s a blow for us. He’s a young full-back who’s come in, broke through and done really well for us. We know that.
“Now it’s time for others to take that mantle and he’ll be back in six weeks.
“It seems a long time now but he’ll be back.”
Lampard added: "We’ve had illness with Anthony Gordon and Yerry Mina. Yerry is over it, Anthony is on the back end of it so we’ll have to consider that.
“Dominic is pretty fatigued after the Brighton game, so we have to consider that as well going into the game so we’ll see whether he’s fit to start.
“Other than that I believe we are where we were [before Brighton].”
Frank Lampard insists his players must "stand up and play for Everton" to overcome their current disappointing run of form.
The Blues return to action on Friday evening when they head to Old Trafford to face Manchester United in the third round of the FA Cup (8pm GMT).
It will be Everton's first contest since Tuesday’s disappointing 4-1 Premier League home defeat to Brighton & Hove Albion, and for the boss, the tie is an opportunity to bounce back with a performance full of courage to deliver for the Club's passionate fanbase.
Speaking ahead of Friday’s trip, Lampard said: “We want to go out and perform well, show performance with a real work-ethic and passion. I have always said that ignites fans in the right way. That’s our responsibility [to do that].
"To play for Everton, you can enjoy things like 5,000 people coming before games, something that helped us get victories last year.
"Sometimes you have to show big courage because they [Evertonians] are a passionate fanbase, and I have got no problem with that.
"At certain times this season we have done that. Do we need the fans sometimes when we are below par? Yes, we do. But at this moment it’s on us to bring them with us, to stand up and play for Everton.
Lampard continued: "I want to be a success at this club. Whatever challenges come, I'll take them head on. It's an honour for me to work for a great club."
Lampard also opened up on ambitions for the January transfer window, admitting the Club are exploring potential permanent and loan deals for this month.
“Loans, obligations, buying players, all things are on the table,” said Lampard.
“We want to improve and help the squad in January, but my job first and foremost has to be about working with the players we have got there now, how can we get a result against Manchester United and Southampton.
"If we can improve the squad then great, it’s not an easy window, everyone knows that, but we’re going to certainly try to improve because it feels like we need that, for sure.”
On the difficulties of trying to recruit early in the January window, the boss said: “There’s a lot of different things that come into play in this window, player agents and so on. People from the outside might look in and think, ‘Why aren’t you doing it this way?’
"We have to look at the best and viable solutions. Of course, I want those solutions because they will help me become a better manager, help us have more competition or get results we haven’t been able to get.
“That’s the importance of recruitment, and there’s no getting away from the fact it’s a huge deal for us, but we’ve also seen in the past decisions like that haven’t always gone right, which can have a negative effect, so we have to be balanced about it.”