2011 All Blacks World Cup winning hero Stephen Donald's next career step has been dealt a blow.

Irish club Ulster has pulled the plug on an already agreed deal, after receiving a medical report on the former Chiefs first five.

Donald, who had been signed to replace returning Brumbies player Christian Lealiifano, suffered an injury while playing in Toshiba's final game of the Japanese season over the weekend.

He's expected to be out for at least a month.

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"Stephen had agreed a short-term deal to join the Province, but he sustained an injury while representing his club in the final game of the Japanese season, which will rule him out for 4+ weeks," the club said.

"The timeline now makes it very difficult to find a suitable replacement, but we will continue to monitor the market."