Nathan Astle has been ruled out of the remainder of the Pakistan tour with a knee injury and will be replaced by Mathew Sinclair.

Astle, regarded as the best batsman in the Kiwi side, had been increasingly troubled by his left knee since the one-day tournament in Sharjah.

After a scan by specialists in Pakistan on Wednesday, he was diagnosed with a tear to the patella tendon.

New Zealand Cricket Operations Manager John Reid said Astle would return home as soon as possible for examination and treatment.

"Nathan will take no further part in the series," said Reid.

Rehabilitation

"We want to get him home for further diagnosis from our medical team and start him on rehabilitation as quickly as possible."

Sinclair will fly out to join the side on Friday.

Astle's injury comes at a most inopportune time for the New Zealanders, with Chris Cairns, Dion Nash, Shayne O'Connor and Shane Bond all injured and captain Stephen Fleming troubled by a stomach bug.

Astle was named New Zealand's cricketer of the summer after the Test win against England at Auckland earlier in April.

He also hit the fastest double century in Test history in the match England won at Christchurch.