Asensio, 23, scored in the game in the United States but was carried off on a stretcher after suffering the injury.

A statement from Real Madrid said: "He has been diagnosed with a rupture of the anterior cruciate ligament and the external meniscus of his left knee.

"The player will be surgically operated in the next few days."

Arsenal were winning 2-0 through goals from Alexandre Lacazette and Pierre-Emerick Aubameyang.

Spain international Asensio scored the equaliser in the 59th minute as a second-half substitute after Gareth Bale had pulled a goal back.

However, he sustained the knee injury five minutes later with the International Champions Cup tie going to penalties, Real winning 3-2.

Reports in Spain suggest Asensio could be out for up to nine months, which could threaten his involvement at Euro 2020 if his country qualify for the finals.

The injury could also have a knock-on effect for Arsenal, who are interested in taking Real midfielder Dani Ceballos, 22, on a season-long loan deal.

After the match, Gunners boss Unai Emery said Asensio's injury could be "bad news for us" and was not sure whether Ceballos would now be needed at Real.