Tim Southee, the New Zealand fast bowler, has been ruled out of the Test series in South Africa because of a thumb injury. He needs surgery for a ruptured ligament and is likely to be sidelined for six-eight weeks.

Southee sustained the injury while diving in the field during a Plunket Shield match between Northern Districts and Wellington at Karori Park. He scored 156 off 130 balls and took seven wickets in Northern Districts' six-wicket win.

"He landed heavily on his thumb while fielding, with scans indicating the ligament has fully ruptured and retracted," New Zealand physio Paul Close said. "After consultation with NZC medical staff and a hand specialist it was decided the best course of action is for him to have surgery.

"He will commence rehabilitation immediately following the procedure, with a view to him returning to cricket during the home summer. The procedure is likely to keep him out of the game for 6-8 weeks."

Southee, who is due to become a father soon, was already missing the Twenty20s in South Africa. New Zealand had not decided on a replacement for Southee, who was their best bowler in the drawn Test series in Sri Lanka, where he took 12 wickets in two matches. Eight of those came in the second Test in Colombo, which New Zealand won by 167 runs.