KEI Nishikori has pulled out of the Australian Open.

The Japanese star - who is currently ranked No.13 in the world - said an ongoing elbow injury had forced him to miss the year's first grand slam and the ATP Cup.

"Unfortunately I have to pull out of the ATP Cup and the Aussie Open," he said on Monday.

"Today, together with my team, we have made this decision as I am still not 100 per cent ready (or) healthy to compete at the highest level.

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"This decision was not taken lightly as Australia is one of my favourite places to compete.

"Together with my team I will keep working hard to be back on court as soon as possible. Thanks for all the support."

Nishikori - who has made four Australian Open quarter-finals - has not played since he fell to Australian Alex de Minaur in the third round of the US Open in August and had surgery on his elbow in the off-season.