All-rounder Carlos Brathwaite has been named as the replacement for Pollard while spinner Narine's place is yet to be filled. All-rounder Pollard withdrew due to "insufficient progress in his rehabilitative work" after injury.
Narine, who was banned for a suspect bowling action, cited "insufficient progress in the rehabilitative work on his bowling action".
Brathwaite was last week bought by Delhi Daredevils for Rs 4.2 crore at the Indian Premier League (IPL) Players Auction in Bengaluru.
"The West Indies Cricket Board (WICB) wishes to advise that two of the 15-member squad selected to participate in the ICC World Twenty20 in India in March to April have withdrawn," a media release from WICB said on Friday (February 12).
"The players and reasons are: 1) On Tuesday February 9, Kieron Pollard withdrew from the squad citing a lack of sufficient progress in his rehabilitative work (injury sustained in December) and hence won't be fit for tournament.
"2) On Friday, February 12, Sunil Narine withdrew citing insufficient progress in the rehabilitative work on his bowling action. He is currently banned from bowling in International Cricket.
"The selectors have today named Carlos Brathwaite to replace Pollard. A replacement for Narine has not yet been named," WICB added.
World T20 will be held in India from 8 March to 3 April. West Indies are in Group 1 (Super 10 Stage) with Sri Lanka, South Africa, England and winner of Group B from first stage.