Japan have been dealt a serious blow ahead of Saturday's Asian Cup final against Australia when inspirational midfielder Shinji Kagawa was ruled out through injury on Wednesday.

Japan's media officer Hideki Kato confirmed the Borussia Dortmund midfielder, who has taken the Bundesliga by storm in his first season in Germany, will miss the final after breaking the fifth metatarsal in his right foot in Tuesday's 3-0 penalty shoot-out semi-final victory against South Korea.

Kagawa missed Wednesday's training session because he was examined in hospital, where the diagnosis confirmed the fracture.

It is not known at this stage how long Kagawa will be out and whether he will remain in Qatar with the squad until the final.

Borussia Dortmund said in a statement on their website that they have been informed of the injury by Japanese officials.

"We immediately contacted the player and he will be returning to Dortmund as soon as possible that our doctor can examine him and ascertain the extent of the injury," a statement said.

Japan, who are seeking an unprecedented fourth continental title, are already without midfielder Daisuke Matsui, who left Qatar earlier after picking up an injury.