Right-arm New Zealand pacer Lockie Ferguson has been ruled out of the ongoing T20I series against Sri Lanka, after fracturing his right thumb at training.

Ferguson sustained the injury while fielding a ball at practice on Saturday night at the Pallekele Cricket Stadium, with an x-ray later revealing a small fracture to the middle joint.

Coach Gary Stead confirmed Ferguson would return home to New Zealand in the coming days.

"It's a shame for Lockie to have to miss this series, especially coming off the back of such an impressive World Cup campaign in England," Stead was quoted as saying according to a New Zealand Cricket media release.

"The thumb has been put in a splint and is expected to take four to six weeks to recover; so we're optimistic he'll be available for the five-game T20 series against England, which starts on November 1 in Christchurch.

The Black Caps, who have taken a 1-0 lead with a five-wicket win in the first T20I played on Sunday, will face Sri Lanka on Tuesday night.