Arsenal manager Arsene Wenger confirmed Mesut Ozil will be sidelined for weeks.
The Germany international joined the national team immediately after Arsenal's defeat against Chelsea with the German medical staff confirming the ligament injury after performing a scan on the player's knee.
"He told me [about the injury] once it was discovered on the scan," Wenger told reporters on Thursday.
"He did not tell me anything during the Chelsea game, I did not know.
"What happened was that at half-time, just before we went out, he had a little pain with his knee but it was not bad. He wanted to go on and I told him, 'If you don't feel well, tell me and I will take you off straight away'.
"He never did that during the whole game, and after I left him on because we were in a position where we needed to score a goal and he can deliver the final ball.
"Then after the game, he went to Germany. With Germany, they thought at the start it was nothing.
"We played on Sunday, on Monday he was off, and on Tuesday they gave him the day off. He was supposed to practice on Wednesday. On Wednesday morning, he said he could still not practice.
"They sent him for a scan, and in this scan they discovered that he a knee ligament injury which is quite serious."
Arsenal host Steve Bruce's Hull City on Saturday hoping to reduce the nine-point gap from leaders Chelsea.
