Chelsea striker Christopher Nkunku is facing knee surgery.

The summer arrival from RB Leipzig broke down in last week's draw with Borussia Dortmund in Chicago.

After initial suggestions were the setback wasn't serious, the Daily Mail says Nkunku is now in need of a knee operation.

And surgery is set to keep the France striker sidelined for "2-3 months".

Blues manager Mauricio Pochettino said at the time: "The doctors are checking him hopefully it is not a big issue but when he fell in the action maybe it was a penalty. Had the chance to score.

"He feels something in his knee but hopefully it is not a big issue and that he can be [back] quickly with the team. Now we need a few days to assess him and until we get back to London it is difficult to know.

"I didn't see the action but it not about to complaining. Always we take some risks because the pitch is not perfect because they are using it for different sports and that is sometimes the risk of the tour, yes.

"But I think it was a bit unlucky in the situation but we cannot complain about the pitch and to blame the pitch for why he suffered the injury. For me it was bad luck."