Corey Anderson's recurring back injury has returned, ending his Tweny20 stint at Somerset and forcing him to return immediately to New Zealand.
The big-hitting left-hander had played a key role in the English domestic T20 competition for Somerset, who sit second in the South Group and are well-placed for the next stage of the competition.
Anderson, 26, has battled ongoing back problems since May last last year, after injuring it in New Zealand's first Test loss to England at Lord's.
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He played in four of New Zealand's five ODIs against India in October, but aggravated his back the following month and returned as a batsman only for the Black Caps Twenty20 series against Bangladesh
On Sunday, Anderson blasted Somerset to a 32-run Duckworth-Lewis victory over Sussex with an unbeaten 41 from 17 balls, which included four fours and three sixes.
Anderson said it was disappointing not to be able to see his contract out.
"I am grateful to Somerset for giving me an opportunity to play cricket in England and only sorry that I've been unable to conclude my stay with them," he said on the club's website.
"However I hope at some point in the future when my back problem has been resolved that I'll be able to return."
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Somerset director of cricket Matt Maynard said Anderson had impressed in his time at Taunton.
"It's disappointing Corey has had to return to New Zealand, particularly in light of what he has achieved during his short time with us," Maynard said.
"During his time here Corey has soldiered on bravely and managed his ongoing stress fracture well but now it needs immediate treatment.
"We have really enjoyed having him around and he has made a positive contribution both on and off the field at the club. Hopefully we will see him again in the future."
Anderson will be replaced by Pakistan opener Fakhar Zaman, who scored a match-winning century against India in the Champions Trophy final in June.
Fakhar will also play four County Championship matches for Somerset.