Alexis Sanchez is likely to return in time for the busy Christmas fixture schedule for Arsenal, but Santi Cazorla is out until the new year after suffering a knee injury at Norwich last Sunday.
Manager Arsene Wenger on Thursday said he did not know the exact prognosis for the pair, but it is believed that playmaker Cazorla's ailment is more long-term than forward Sanchez's hamstring problem.
Wenger is convinced Arsenal are capable of coping in the absence of two of their most influential players.
"It's always a disappointment to lose the players at an important moment of the season," Wenger said on arsenal.com.
"But on the other hand, it's a great challenge to take for the team and a great opportunity to show that we are ready for a fight and we can deal with it.
"We prepared ourselves to go through periods like that, and I'm convinced the players are ready."
Despite his comments, Wenger could come under pressure from supporters to recruit during the January transfer market with his squad rocked by injuries.
Chile forward Sanchez suffered his hamstring injury in the 1-1 draw at Carrow Road, while Spain midfielder Cazorla finished the game "playing on one leg" after suffering a blow to his knee.
Wenger said "we don't know how long they will be out for" when discussing the injuries on Thursday, but may provide an update at his Friday morning media conference to preview Saturday's Premier League clash with Sunderland.
The Gunners are fourth, two points behind leaders Manchester City, entering this weekend's fixtures, while their hopes on making the Champions League last 16 - an achievement they have managed for each of the last 15 seasons - rest on beating Olympiacos by two clear goals in Greece next week.
Following the draw at Norwich, Wenger faced criticism for selecting Sanchez.
"I would have rested him but he felt perfectly all right before the game and he declared that he had no problem," Wenger said.
Laurent Koscielny (hip) had to be substituted at the weekend, but could feature against the Black Cats. The France defender and Theo Walcott will face late fitness tests.
England forward Walcott suffered a calf injury at Sheffield Wednesday in October. Left-back Kieran Gibbs is back in contention after missing the Norwich trip with a calf injury.
Wenger added: "We will make a decision on Saturday on Koscielny and Walcott, they could both make the squad. Gibbs is available again for the weekend."
Mikel Arteta suffered a calf injury against West Brom last month and the length of his absence is still to be determined.
Midfielders Jack Wilshere (broken leg), Francis Coquelin (knee), Tomas Rosicky (knee) and forward Danny Welbeck (knee) are all out.
Arsenal's only win in five games in November came against Dinamo Zagreb in the Champions League.
"We have gone through a little bit of a bad spell in recent games, but we are two points off the top (in the league)," Wenger added.
"The great opportunity for us is that, despite that bad spell, we are very close. That's why it's important that we keep our confidence high and our determination high, and start winning again.
"We want the crowd to be behind the team and help us to do it."