Arsenal coach Mikel Arteta said winger Bukayo Saka will be out for “several weeks” due to a hamstring injury.
The England striker was forced off during Saturday's match 5-1 win over Crystal Palace He left Selhurst Park on crutches.
Saka (23 years old) scored nine goals and provided 13 assists in 24 matches in all competitions this season.
“It doesn't look good,” Arteta said. “He will be out for several weeks.
“That's the thing. He's injured and we can't change him. We'll use this time now to help him.”
Arteta said that he is “collecting some ideas” to deal with Saka's absence, and that Arsenal has experience in dealing with the absence of key players after losing its captain, Martin Odegaard, to injury this season.
Asked if Saka had “torn” something in his hamstring, Arteta replied: “Yes. Maybe there are ways to prevent the injury.
“There are a lot of factors. We look at everything and what we can do differently.”
Arteta said Saka was “devastated” and “really emotional” after discovering the severity of his injury.
Asked whether the crowded fixture list played a role in Saka's injury, Arteta replied: “It's probably more of an accumulation (of matches) as people like Declan (Rice) and Bukayo played more than 130 matches in three seasons.”
The Spanish coach also confirmed that Raheem Sterling will be absent from the field for a period after suffering a knee injury.
“He will be gone for weeks,” Arteta said. “He needs more tests tomorrow.”
The Gunners will next face Ipswich at the Emirates Stadium in the league on December 27 (20:15 GMT).